Jack Castle
“Clever, hard-working, a team player, most and plainly destined for great things.”
Legal 500 2026
- Call
- 2018
Jack has a busy practice in line with Chambers’ expertise. He has experience ranging across commercial, financial services, competition/subsidy control, employment, human rights and public law and public international law. He acts in both individual and group claims.
He has appeared as sole or leading counsel in the Court of Appeal, High Court, Upper Tribunal and the Employment Appeal Tribunal, conducted oral advocacy (led) in the Supreme Court, and acts in the European Court of Human Rights. Many of his cases involve issues of retained EU/assimilated law and the impact of the UK-EU Withdrawal Agreement.
Notable instructions include:
- Pan-NOx Group Litigation – Acting for Mercedes Benz the NOx emissions litigation, including at the “KBA” (EU/regulatory) and “PDD” (technical) trials (one of The Lawyer’s Top 20 Cases of 2025).
- Wright & oths v BTC Core & Oths – Claim involving intellectual property rights in the main Bitcoin blockchain and the identity of its pseudonymous creator ‘Satoshi Nakamoto’ (one of The Lawyer’s Top 20 Cases of 2024).
- Simkova v Secretary of State for Work and Pensions – Supreme Court appeal on the classification of the welfare benefit Universal Credit in EU law and scope of the Withdrawal Agreement.
- Cygnet Healthcare v CQC – Judicial review and A1P1 damages claim against the healthcare regulator for inspection failures.
- EdTech Firm v Ex-Manager and Rival EdTech – Claim by an EdTech start-up in conspiracy, breach of confidence and database rights against a former senior manager.
- Gunnooa v United Kingdom, Byles v United Kingdom – Application to the ECtHR concerning discriminatory access to bereavement payments on the basis of marital status.
- BioTech procurement – Advising central government on competition and subsidy aspects of a proposed public-private partnership.
- J v Secretary of State for Work and Pensions – Appeal concerning the interaction of the UK-EU Withdrawal Agreement, UK-EU Trade and Cooperation Agreement, and a series of treaties between the UK and New Zealand on reciprocal entitlement to state pensions.
- Private Equity Employee v Fund – Confidential 7-figure matter regarding alleged discrimination and negative references by a former employer.
- Collector v Art Gallery – Advising on matters arising out of the purchase of a David Hockney.
- M v Secretary of State for Work and Pensions – Appeal concerning discriminatory protection for victims of domestic violence and compliance with the Istanbul Convention.
He is ranked in multiple practice areas by the Legal 500 and is a member of the Attorney General’s Public International Law panel.
Prior to his career at the bar Jack worked at an international auction house and a commercial art gallery. He is a non-executive director of Fitzcarraldo Editions, an independent publishing house.
For more information about the way barristers at Henderson Chambers work, including our terms of engagement, fee transparency statement and our complaints process, please click here. Barristers are regulated by the Bar Standards Board.
Please click here for a copy of Jack Castle’s privacy policy.
Expertise
Administrative and Human Rights
Jack undertakes the full spectrum of public law work as both junior and sole counsel. He is ranked in the Legal 500 for his work in Administrative Law and Human Rights.
His public law work spans a variety of areas, from regulation of financial services and healthcare to freedom of information, data protection, environmental law and national security cases. He has also advised on a number of damages claims under A1P1 arising out of unlawful regulatory action.
He has a particular interest in social security, welfare benefits, and their interaction with free movement rights. He regularly represents claimants on a publicly funded or pro bono basis in both statutory appeals and judicial reviews.
Representative cases
grid list-
Re: Pension Protection Fund
Advising on a potential challenge involving the classification of the assets of the Pension Protection Fund for public accounting purposes and compliance with fiscal rules (led by Henry Warwick KC).
-
Re: Council Tax Reduction Schemes
Acting and advising in a number of rationality, Equality Act and Human Rights challenges to Council Tax Reduction Schemes (with Tom Royson and Alexa Thompson).
-
Gunnooa v United Kingdom, Byles v United Kingdom
Acting in an application to the European Court of Human Rights for two individuals denied widowed parent’s allowance because they were unmarried at the time of their partners’ death (led by Adam Heppinstall KC).
-
Simkova v Secretary of State for Work and Pensions [2025] UKSC 41
Acted for a Slovakian national in an important appeal concerning entitlement to the child element of Universal Credit, raising issues concerning the interaction of Universal Credit with EU Regulation 883/2004 on the coordination of social security systems (led by Thomas de la Mare KC). Jack represented Ms Simkova before the Upper Tribunal as sole counsel ([2023] UKUT 44 (AAC)) and made oral submissions before the Court of Appeal and Supreme Court.
-
R. (on the application of Cygnet Health Care Ltd) v Care Quality Commission
Instructed in a commercial judicial review involving alleged apparent bias by a regulator’s inspector and a linked A1P1 damages claim (led by Patrick Green KC). Cygnet has been successful in its judicial review – [2025] EWHC 1 (Admin).
-
R (LL and AU) v Trafford MBC [2025] EWHC 2380
Acted in a successful judicial review of a council tax reduction scheme, which irrationally and discriminatorily double-counted certain disability-related benefit as income, including what is thought to be the first finding of indirect discrimination by association by a court of record (led by Tom Royson).
-
GN v Secretary of State for Work and Pensions, IMA and the3million intervening
An important Upper Tribunal appeal concerning the correct interpretation of Article 10 “personal scope” of the Withdrawal Agreement and interim protection under Article 18(3) while an application under the EUSS is pending. Instructed for the3million by the Public Law Project (led by Tom Royston).
-
R(UMAPS) v NHS England, Secretary of State for Health and Social Care and Professor Gillian Leng
Ongoing judicial review of the decision to implement the findings of the Leng Review concerning the scope of practice of physician and anaesthesia associates (led by Patrick Green KC).
-
R(L) v Service Complaints Ombudsman for the Armed Forces [2024] EWHC 1094 (Admin); [2024] A.C.D. 76
Appeared as sole counsel for the interested party, the Ministry of Defence, in a judicial review concerning the jurisdiction of the Service Complaints Ombudsman for the Armed Forces.
-
Secretary of State for Work and Pensions v MA [2024] UKUT 131 (AAC); [2024] P.T.S.R. 1243
Appeared as sole counsel in an Upper Tribunal appeal concerning whether selling stolen goods is considered “work”, and if money obtained therefrom is “income”, for the purposes of entitlement to income-related Employment and Support Allowance. Permission to appeal has been granted by the Court of Appeal.
-
Carter v Westminster City Council and City of London Corporation [2025] UKUT 054 (AAC); [2025] UKUT 055 (AAC)
Successfully represented the requester as sole counsel on appeal in a matter concerning disclosure of business rates information by two London councils under the Freedom of Information Act.
-
Re: Regulation of Advertising
Instructed, as sole counsel, by a well-known trade union in potential judicial review proceedings arising out of potential regulatory action relating to advertising, raising issues of jurisdiction (including a “precedent fact” challenge) and Article 10 ECHR. The regulator dropped its investigation following pre-action correspondence.
-
LR (by her litigation friend RR) v Secretary of State for Work and Pensions
Instructed as sole counsel in the Upper Tribunal in a matter concerning the renewal process for Disability Living Allowance and Thlimmenos discrimination.
-
Private Healthcare Provider v CQC
Acted for a private healthcare provider challenging conditions placed on registration by the CQC in breach of legitimate expectations and the Tameside duty. Notice withdrawn after grounds of appeal filed.
-
GP v Secretary of State for Work and Pensions
Acting in an appeal to the Upper Tribunal for a pensioner deprived of state pension while held on remand and subsequently given a suspended sentence, raising statutory interpretation and human rights issues (Articles 6, 7, A1P1 and 14).
-
Advice on duties under the Care Act 2014 in public and private law
Advised a local government body on interlinking matters involving real property, irrationality and substantive legitimate expectations relating to its duty/power to offer a property disregard or Deferred Payment Agreement to an adult in a care home who held an interest in her home as a tenant in common.
-
A v University B
Instructed, as sole counsel, by a Paralympic athlete alleging disability discrimination in the assessment and non-award of their degree and the University’s internal appeals process. Settled.
-
Negligence/A1P1 and Article 14 claim against a professional regulator
Claim in negligence and breach of A1P1, both independently and read with Article 14, concerning availability of professional indemnity insurance.
-
Advice on representative claim against compensation scheme
As sole counsel, advised potential claimants in a proposed action against a compensation scheme.
-
Advice regarding approval for public office
Assisted leading counsel in advising a government department on issues surrounding special approval to a public office, including the court’s approach to review of religious judgments and Article 6 ECHR.
Commercial
Jack’s commercial practice includes complex disputes arising out of banking and finance, frauds, intellectual property and cryptocurrency, as well as confidential information, restraint of trade and general contractual matters.
Many of his cases arise in the context of partnerships, joint ventures or the employment relationship. He also acts in cases involving secret commissions, bribery, breach of fiduciary duty and unjust enrichment.
He frequently acts in applications for urgent and pre-action injunctions, including proprietary and freezing injunctions, in areas from team-move litigation to real property investments.
He is also instructed in commercial matters raising other areas of law, particularly public law and financial regulation.
In 2021 Jack was a judicial assistant in the Commercial Court, chiefly to Cockerill J (as she then was).
Representative cases
grid list-
Pan-NOx Emissions Group Litigation
Instructed for the Mercedes-Benz Defendants in what are thought to be the largest GLO proceedings currently before the English courts. Jack appeared (led by Helen Davies KC) in the “KBA Trial”, concerning whether the English court is bound by decisions taken by the Kraftfahrt-Bundesamt pursuant to the EU regime before, during and post-Brexit ([2024] EWHC 2904 (KB)), and appeared in the technical “PDD trial”, heard in winter 2025.
-
Wright & Oths v BTC Core & Oths
Instructed in a claim concerning the identity of the pseudonymous founder of Bitcoin ‘Satoshi Nakamoto’ and intellectual property rights in its blockchain. This includes the ‘identity issue’ trial deciding the identity of Satoshi – [2024] EWHC 1198 (Ch) – one of The Lawyer magazine’s Top 20 Cases of 2024 (led by Terence Bergin KC).
-
Partnership dispute
Instructed as sole counsel in the High Court in a long-running dispute concerning a partnership formed to invest in residential property, involving allegations of misuse of partnership assets and breach of constructive trust. Jack secured urgent, without notice proprietary relief to prevent imminent disposal of partnership property ([2023] EWHC 2647 (Ch)).
-
Wright v McCormack [2024] EWHC 1735 (KB)
Instructed in an application for a freezing order based on allegations that costs orders had been procured by fraud (led by Adam Baradon KC).
-
Advice on fraud by an employee and ownership of intellectual property
As sole counsel, advised a large manufacturing concern concerning apparently fraudulent payments made by employees, potential computer hacking by those employees, and a dispute over intellectual property rights in software made during the course of employment.
-
Breach of restrictive covenant and misappropriation of Facebook accounts
Instructed as sole counsel in the High Court in a claim involving a number of employees who retained work Facebook accounts following resignation in order to start a new competing business.
-
Team move in the recruitment industry
Instructed, as sole counsel, in a High Court pre-action injunction and claim involving misuse of confidential information on behalf of (and diversion of business to) a competitor, and breach of restrictive covenant.
-
Breach of director’s duties and diversion of profits
Instructed, as sole counsel, in a High Court matter alleging appropriation of significant sums from the business by the company secretary and their accomplice, listed for an 8-day trial in 2024. Settled at mediation.
-
Matter involving sale of artwork
Instructed as sole counsel in a contractual dispute by a buyer of a significant work of Modern British Art.
-
Advice on jurisdiction and choice of law
Instructed to advise on the correct construction of a contract for financial services with competing jurisdiction and choice of law clauses in favour of both English and Lithuanian law and courts.
-
Breach of contract arising out of provision of agency workers
Instructed as sole counsel in a complex £500,000 breach of contract claim where a recruitment agency supplied agency workers to a client, which then recruited them as employees.
-
Claim involving fire caused by electric bike battery
Instructed, as sole counsel, on behalf of a film production company and its director in a £1.5m claim arising out of a fire caused by the battery of an electric bike. Settled post-issue.
-
Claim concerning allegedly defective title to goods bought at auction
Instructed for the Defendant purchaser of a piece of large plant machinery, defending a claim by a third party that it was auctioned without the consignor having good title.
-
Claim against leaseholders under the Electricity Act 1989
Acted successfully for a “Big Six” energy supplier in relation to the liability of commercial lead-tenants for the consumption of insolvent lessees under the Electricity Act 1989.
-
Dispute concerning “feed-in” tariffs
Instructed by a “Big Six” energy supplier in relation to a dispute concerning renewable energy feed-in tariffs.
Competition and Subsidy Control
Jack acts in cases involving EU and UK aspects of competition law and subsidy control for both private parties and state bodies.
He has experience in matters ranging from financial products and insurance to biotech and medical research.
Before joining chambers Jack was Visiting Lecturer in EU Law at City, University of London. He will be called to the Bar of Ireland in summer 2027.
Representative cases
grid list-
Pan-NOx Emissions Group Litigation
Acted for the Mercedes-Benz Defendants in what is thought to be the largest GLO proceedings before the English courts. The claim includes a number of alleged cartels based on alleged restriction on technical development.
-
A matter regarding professional indemnity insurance
Acting for a regulated professional challenging regulatory restrictions on the potential sources of professional indemnity insurance as a breach of Chapter 1 and Chapter 2.
-
Advising on the TCA and Northern Ireland Protocol
Advised central government on the subsidy implications of grants to improve social housing, under the TCA, Subsidy Control Act 2022 and Northern Ireland Protocol.
-
Advising Government departments on Covid-19 issues
Seconded to the Government Legal Department to advise a range of Government departments on competition and state aid issues.
-
A financial services group action
Assisted in advising on a potential state aid and/or public law defences to the setting of interest rates on certain financial products after the nationalisation of Northern Rock.
Employment
Jack regularly acts in High Court employment-related commercial matters involving team moves, breaches of contract and restrictive covenant, and intellectual property issues arising in this context, including applications for interim injunctive relief and civil frauds involving diversion of company funds and property.
He also appears as sole counsel in statutory Employment Tribunal claims for unfair dismissal, whistleblowing, discrimination, failure to make reasonable adjustments, holiday pay and unlawful deduction of wages. This includes potential lifetime loss of earnings cases with values above £1m.
He has further experience of the TUPE regime, worker status, the agency workers regulations, pensions and bonus disputes, and public law issues arising in employment matters. He represents both employees and employers.
He has also advised on EU/Withdrawal Agreement social security coordination in the employment context, where employees are located abroad.
Representative cases
grid list-
Tech Company v Ex-Employee and Competitor
Acting for a tech start-up against a former senior manager using confidential information for the benefit of a rival (led by Adam Baradon KC).
-
R(UMAPS) v NHS England, Secretary of State for Health and Social Care and Professor Gillian Leng
Ongoing judicial review of the decision to implement the findings of the Leng Review concerning the scope of practice of physician and anaesthesia associates. Jack is instructed to deal with Article 11 ECHR aspects (led by Patrick Green KC).
-
Individual v Investment Firm
Acted in Employment Tribunal proceedings for an individual in the financial services sector seeking lifelong loss of earnings and payments of carried interest (led by Jeremy Lewis KC and Giles Powell).
-
Hilton Foods Solutions v Wright [2024] I.C.R. 862; [2024] I.R.L.R. 532
Acted successfully as lead counsel in the EAT in a matter concerning the meaning of “sought” to take parental leave in the Maternity and Parental Leave etc. Regulations 1999.
-
Breach of restrictive covenant and misappropriation of Facebook accounts
Instructed as sole counsel in the High Court in a claim involving a number of employees who retained work Facebook accounts following resignation in order to start a new competing business.
-
R(L) v Service Complaints Ombudsman for the Armed Forces [2024] EWHC 1094 (Admin); [2024] A.C.D. 76
Appeared as sole counsel for the interested party, the Ministry of Defence, in a judicial review concerning the jurisdiction of the Service Complaints Ombudsman for the Armed Forces.
-
Team move in the recruitment industry
Instructed, as sole counsel, in a High Court pre-action injunction and claim involving misuse of confidential information on behalf of (and diversion of business to) a competitor, and breach of restrictive covenant.
-
Breach of director's duties and diversion of profits
Instructed, as sole counsel, in a High Court matter alleging appropriation of significant sums from the business by the company secretary and their accomplice, listed for an 8-day trial in 2024. Settled at mediation.
-
Phillips v National Grid Gas Plc
Instructed in an action for negligent failure by an employer to give a correct report of the reason for an employee’s dismissal to the pension scheme, leading to loss of pension from that scheme (led by Adam Heppinstall KC).
-
Union Member v Trade Union
Instructed as sole counsel in a claim concerning the right to be represented by a lawyer in union disciplinary proceedings under the Defendant Trade Union’s rules.
-
Advice on jurisdictional issues relating to maternity leave and pay
Advised an organisation on the jurisdictional scope of rights to maternity leave and maternity pay, including issues relating to social security coordination under the Withdrawal Agreement.
-
Breach of contract arising out of provision of agency workers
Instructed as sole counsel in a complex £500,000 breach of contract claim in which a recruitment agency supplied agency workers to a client, which then recruited them as employees.
-
Health and safety/whistleblowing claim against private hospital
Successful in a 4-day constructive dismissal and detriment claim against a private healthcare provider on behalf of a therapist who was refused permission to conduct remote consultations in the first national Covid lockdown. Case was covered in the Evening Standard.
-
Disability and victimisation claim
Instructed in a complex disability discrimination claim involving a data breach arising out of the claimant being allowed to work from home, and allegedly being forced to make a false confession.
-
Disability discrimination claim against national charity
Instructed to represent the ex-Director of Communications in a claim for discriminatory dismissal due to the effects of hypothyroidism, depression and anxiety in a 5-day final hearing. Matter settled before trial.
-
Positive discrimination advice
Advised a company on its ability to positively discriminate on grounds of race/ethnic background in recruitment.
-
Claim against English company by employee of foreign branch
Unlawful deduction of wages claim involving issues of “limb (b) worker” status and the applicability of foreign law.
-
Discrimination, whistleblowing and health and safety claim against a government department
Acted for the successful Claimant in a 4-day liability hearing involving complex and interlinking constructive discriminatory, whistleblowing and health and safety dismissal claims. Also successfully required the respondent to give specific disclosure of documents the existence of which it had previously denied. Claim settled shortly before the remedy hearing for a six-figure sum, including a substantial sum for loss of pension and provisions accounting for foreign taxation.
-
Advice regarding approval for public office
Assisted leading counsel in advising a government department on issues surrounding special approval to a public office, including the court’s approach to review of religious judgments and Article 6 ECHR.
Financial Services
Jack is regularly instructed by major UK lenders for his expertise in financial services.
He regularly acts in matters involving allegations of mis-selling, secret commissions and fiduciary duties, suspension of bank accounts due to fraud and/or money laundering, push-payment frauds, scams and disputes over credit referencing information.
He also acts in cases involving the Money Laundering, Terrorist Financing and Transfer of Funds (Information on the Payer) Regulations 2017, and has extensive experience of group litigation in financial services, including property investments, mortgage interest rates, solar panels, payment protection insurance, motor finance commissions and breaches of fiduciary duties by mortgage brokers.
He has particular expertise in financial regulation and compliance with the FCA Handbook, and was seconded to the FCA to assist with investigations into the adequacy of advice given to customers transferring out of Defined Benefit pensions. He also has experience of matters at the intersection of employment law and regulatory issues in the financial services sector.
Jack was editor of the ‘Assignment & Participation of Loans’ chapter of Practical Lending & Security Precedents for many years, and is the author of the ‘FCA Authorisation’ chapter in Consumer Credit Law and Regulation (2024).
Representative cases
grid list-
Re: Pension Protection Fund
Advising on a potential public law challenge involving the classification of the assets of the Pension Protection Fund for public accounting purposes and compliance with fiscal rules (led by Henry Warwick KC).
-
Howard v GE Money Mortgages Ltd and Promontoria [2025] EWCC 18
Acted on appeal for the assignee of a mortgage in a matter concerning when limitation begins to run against an assignee of a credit agreement for the purposes of s.140A Consumer Credit Act 1974.
-
Advice on jurisdiction and choice of law
Instructed to advise on the correct construction of a contract for financial services with competing jurisdiction and choice of law clauses in favour of both English and Lithuanian law and courts.
-
Appeal against "fit and proper" assessment for AML purposes
Instructed as sole counsel by HMRC defending an appeal against the “fit and proper person” decision under the Money Laundering, Terrorist Financing and Transfer of Funds (Information on the Payer) Regulations 2017.
-
A v B Ltd and C
Instructed as sole counsel in a claim against a claims management company alleging breach of the general prohibition and seeking compensation under section 26 FSMA.
-
Advice on s.138D action and FOS complaint
Advising an investor on potential breaches of the FCA Handbook and the FPO by an Appointed Representative with a view to recovering their investment in a failed £2m property venture.
-
FCA Defined Benefits Pensions Enforcement
Assisted the FCA in a large-scale enforcement action arising out of inadequate provision of advice surrounding transfers out of defined benefits pension schemes.
-
Claim against major online bank
Instructed as sole counsel defending a major online bank against an alleged breach of the Quincecare duty and breach of the Payment Services Regulations 2017 arising out of an alleged authorised push-payment fraud.
-
Claim for frustration of a credit agreement
Acting for a major lender in a claim alleging frustration of a credit agreement due to the COVID-19 pandemic.
-
Claim in breach of fiduciary duty against two major lenders
Acting for a bank in a claim for breach of fiduciary duty and unjust enrichment alleging secret commissions were made to a broker.
-
Advice on regulatory authorisation
Advising on the process by which authorisation to purchase a bank could be objected to due to suspected money laundering.
-
A financial services group action
Assisted in advising on a potential state aid and/or public law defences to the setting of interest rates on certain financial products.
-
Advice on FCA compensation
Assisted in a matter concerning whether redress paid for prospective Plevin claims under the FCA scheme barred further civil claims.
-
Gibbs v Information Commissioner and Financial Reporting Council (EA/2017/0284)
Represented the Appellant in an appeal concerning the applicability of the Freedom of Information Act to the FRC’s scheme for the regulation of statutory auditors in the immediate aftermath of the 2008 financial crisis.
Group Actions
Jack has experience of group claims involving financial mis-selling, medical devices and medications, consumer rights, environmental disasters and international tort claims, including what is reportedly the biggest group action in English legal history arising from the collapse of the Fundão dam in Brazil and in the “Deiselgate” litigation, where he acts for Mercedes Benz.
This has included issues ranging from choice of law and management of the claimant group to novel points in the law of tort, parent company liability, and the immunity of international organisations.
He has also advised and assisted in advising on the preliminary and pre-action stages of a number of group actions, including considerations of the most suitable substantive causes of action to certain group claims, organisation of the claimant cohort, strategy, tactics, and potential funding issues.
Representative cases
grid list-
Pan-NOx Emissions Group Litigation
Instructed for the Mercedes-Benz Defendants in what are thought to be the largest GLO proceedings currently before the English courts. Jack appeared (led by Helen Davies KC) in the “KBA Trial”, concerning whether the English court is bound by decisions taken by the Kraftfahrt-Bundesamt pursuant to the EU regime before, during and post-Brexit ([2024] EWHC 2904 (KB)), and appeared in the technical “PDD trial”, heard in winter 2025.
-
Medical device group action
Instructed by the manufacturer in a claim concerning a permanent birth control device (led by Toby Riley-Smith KC).
-
A consumer rights group action
Instructed to advise on a group claim involving deception by traders relating to past usage of second-hand goods raising complex issues of European-derived law (including whether certain domestic legislation is an implementation of an EU directive and indirect effect). This included advising on the suitability of certain causes of action for group litigation and organisation of a claimant cohort, as well as strategy, merits and quantum (led by Nazeer Chowdhury).
-
Group action concerning mis-selling of property investments
Assisted in advising the claimant group following the collapse of a US property investment scheme, on issues including forum and choice of law, attribution of knowledge to a company, joint liability in tort and practical issues concerning how to arrange the claimant group.
Information and Data Protection
Jack has extensive experience of public and private law claims involving data protection, information access rights, breach of confidence and intellectual property/database rights, ranging from statutory appeals to urgent injunctive relief.
He acts for journalists, businesses, government departments and financial institutions.
He is ranked as a leading junior in Data Protection.
Representative cases
grid list-
Carter v Westminster City Council and City of London Corporation [2025] UKUT 054 (AAC); [2025] UKUT 055 (AAC)
Successfully represented the requester as sole counsel on appeal in a matter concerning disclosure of business rates information by two London councils under the Freedom of Information Act. Jack appears as sole counsel in the Court of Appeal.
-
Wright & Oths v BTC Core & Oths
Instructed in a claim concerning the identity of the pseudonymous founder of Bitcoin ‘Satoshi Nakamoto’ and intellectual property rights in its blockchain. This includes the ‘identity issue’ trial deciding the identity of Satoshi – [2024] EWHC 1198 (Ch) – one of The Lawyer magazine’s Top 20 Cases of 2024 (led by Terence Bergin KC).
-
Walawalkar v Information Commissioner, Maritime and Coastguard Agency [2025] UKUT 105 (AAC); [2025] 1 WLR 3418
Acted as sole counsel in a complex Freedom of Information Act appeal for a Liberty Investigates journalist seeking transcripts of distress calls made from small boats to the Coast Guard. This is an important authority on the s.11 FOIA duty to give information in a certain form, and the correct approach when that choice of form may change which substantive exemptions are relevant.
-
[Confidential] v Ministry of Defence
Claim concerning alleged breach of the UK GDPR by the Ministry of Defence by disclosing the name of a soldier in a request under the Freedom of Information Act (led by George Mallet).
-
[Confidential] v [Financial Institution]
Acted for a financial institution in a claim alleging information being wrongfully passed to a credit reference agency.
-
Advice on bulk data collection
Advised a public authority on bulk data collection and the impact of Article 8 ECHR and UK GDPR (led by Christopher Knight KC).
-
[EdTech Firm] v [Ex-Employee] and [Rival EdTech]
Jack acts for a successful EdTech startup against an ex-employee and rival EdTech startup in a claim for conspiracy and breach of confidence arising out of the removal of large amount of proprietary information by the Ex-Employee and the alleged arrangement to use that information in the new business.
-
Advice on fraud by an employee and ownership of intellectual property
As sole counsel, advised a large manufacturing concern concerning apparently fraudulent payments made by employees, potential computer hacking by those employees, and a dispute over intellectual property rights in software made during the course of employment.
-
Breach of restrictive covenant and misappropriation of Facebook accounts
Instructed as sole counsel in the High Court in a claim involving a number of employees who retained work Facebook accounts following resignation in order to start a new competing business.
-
Gibbs v Information Commissioner and Financial Reporting Council (EA/2017/0284)
Represented the Appellant in an appeal concerning the applicability of the Freedom of Information Act to the FRC’s scheme for the regulation of statutory auditors in the immediate aftermath of the 2008 financial crisis.
-
Gibbs v Information Commissioner and FCO (EA/2017/0258 & 0275)
Represented the Appellant in a 3-day Freedom of Information Act appeal relating to the decision to approve export of a warship to an individual in the Niger Delta with a history of militancy. Raised issues of prejudice to international relations, ongoing criminal investigations and the Article 6 rights of potential defendants, judicial deference to Government witnesses, and the scope of the Article 10 right to receive information.
Procurement
Jack has a particular interest in procurement, and acts for contracting authorities and economic operators in procurement and subsidy control matters.
In 2020 he was seconded to the Government Legal Department’s ‘Covid Cell’, advising on a variety of important procurement and state aid matters relating to the Covid-19 pandemic, including procurement of mass testing capacity and vaccines.
He is a procurement specialist member of LexisNexis’ Q&A Panel.
Representative cases
grid list-
Challenge by economic operator to award of temporary workers contract
Advised as sole counsel on a challenge to an award of a contract to provide temporary staff on the basis of the potential bias of one of the award panel.
-
Advising central government on pre-tender issues in establishing an arbitration scheme
Advised a central government department on issues surrounding a proposed tender for a compulsory arbitration scheme and the compliance of that scheme with Article 6 ECHR.
-
Advising an economic operator on a £150m procurement
Advised an economic operator in a potential challenge to the marking and award of a contract in the justice sector.
Public International and EU Law
Jack has extensive experience in public international law, European Union law and retained EU law matters as they arise across his areas of practice. This includes interpretation of treaties, immunities, the effects of unincorporated international instruments, acts of state and the international obligations of the European Union.
He is also frequently involved in matters concerning the ECHR, both domestically and in Strasbourg (for more details see “Public and Regulatory” above).
Before joining chambers, Jack was Visiting Lecturer in EU Law at City, University of London. He is a member of the Attorney General’s Public International Law panel.
Representative cases
grid list-
Gunnooa v United Kingdom, Byles v United Kingdom
Acting in an application to the European Court of Human Rights for two individuals denied widowed parent’s allowance because they were unmarried at the time of their partners’ death (led by Adam Heppinstall KC).
-
Pan-NOx Emissions Group Litigation
Instructed (led by Helen Davies KC) in the “KBA Trial”, concerning whether the English court is bound by decisions taken by the Kraftfahrt-Bundesamt pursuant to the EU regulatory regime before, during and post-Brexit and consideration of UN/ECE product standards ([2024] EWHC 2904 (KB)).
-
J v Secretary of State for Work and Pensions
Appeal concerning the interaction of the UK-EU Withdrawal Agreement, UK-EU Trade and Cooperation Agreement, and a series of treaties between the UK and New Zealand on reciprocal entitlement to state pensions.
-
GN v Secretary of State for Work and Pensions, IMA and the3million intervening
An appeal concerning the correct interpretation of Article 10 “personal scope” of the Withdrawal Agreement and interim protection under Article 18(3) while an application under the EUSS is pending as a matter of treaty interpretation on public international law principles. Instructed for the3million by the Public Law Project (led by Tom Royston).
-
Simkova v Secretary of State for Work and Pensions [2025] UKSC 41
Acted for a Slovakian national in an important appeal concerning entitlement to the child element of Universal Credit, raising issues concerning the interaction of Universal Credit with EU Regulation 883/2004 on the coordination of social security systems (led by Thomas de la Mare KC). Jack represented Ms Simkova before the Upper Tribunal as sole counsel ([2023] UKUT 44 (AAC)) and made oral submissions before the Court of Appeal and Supreme Court.
-
Advice on Direct Effect of EU Directives
Advised a central government department on whether an EU Directive had direct effect post-Brexit.
-
Gibbs v Information Commissioner and FCO (EA/2017/0258 & 0275)
Represented the Appellant in a 3-day Freedom of Information Act appeal relating to the decision to approve export licenses of a warship to an individual in the Niger Delta with a history of militancy.
What the directories say
“Jack has an impressive grasp of EU relations law, particular the Withdrawal Agreement and all aspects of EU social security coordination, putting him in a very small cohort of people with this knowledge. He is clever, hard-working, a team player, most and plainly destined for great things.”
Legal 500 2026
“Jack is not afraid to make legally creative arguments. He has an engaging style of advocacy which holds the judge's attention.”
Legal 500 2026
“Jack is intellectually strong and gets to grips with a matter very quickly. He is a confident advocate and has a good manner with judges when put on the spot.”
Legal 500 2025
“Jack is a very effective cross-examiner and an impressive, unperturbed advocate.”
Legal 500 2024
News and articles
Legal 500 2027 Guide – Top Tier Rankings for...
ALERTER A New Theory of Harm? Case T-1139/23,...
Appointments to the Attorney General’s Panel of...
Pan-NOx Litigation: PDD Trial Judgment Handed Down
Adam Heppinstall KC & Jack Castle successful in...
Jack Castle appointed to the Attorney General’s...
Instructing Jack Castle
If you require help or advice please contact our clerking team
Call +44 (0)20 7583 9020
or email
- Attorney General’s Public International Law ‘C’ Panel (effective 1 January 2026)
- Attorney General’s C Panel
- Centre for Women’s Justice, Legal Reference Panel
- Panel Member, Advocate
- Contributing Editor of ‘Judicial Review, Statutory Review and Habeas Corpus’ in Butterworth’s Civil Court Precedents
- Author of the ‘FCA Authorisation’ chapter in Consumer Credit Law and Regulation (2024)
- Former Editor of ‘Assignment & Participation of Loans’ in Practical Lending & Security Precedents
- Contributor to Lexis®PSL Public Law
- Procurement Specialist Contributor to LexisNexis Q&A panel
- ALBA
- Bar European Group
- Competition Law Association
- COMBAR
- Employment Lawyers Association
- Financial Services Lawyers Association
Education
- BA English Literature, Bristol University, First Class
- MSt. English Literature Post-1900, University of Oxford, Distinction
- GDL, City Law School, University of London, Distinction
- BPTC, City Law School, University of London
Scholarships
- Major Scholarship (BPTC), Inner Temple (2017)
- Duke of Edinburgh Entrance Award, Inner Temple (2017)
- Postgraduate Scholarship (BPTC), City Law School (2017)
- Kalisher Trust Advocacy Training Programme (2017)
- Exhibition (GDL), Inner Temple (2016)
- Postgraduate Scholarship (GDL), City Law School (2016)
All members of Chambers are registered with the Bar Standards Board of England and Wales. For our standard contractual terms click here.
For more information about the way barristers at Henderson Chambers work, including our fee transparency statement and our complaints process, please click here.
Bar Council Number: 70906
VAT Registration Number: 356025609
Legal Status: Barrister
Professional Insurance: All members of Chambers have professional liability insurance provided by the Bar Mutual Indemnity Fund Ltd. Territorial coverage is world-wide and subject to the term of the Bar Mutual. Click here for details.
Regulated by the Bar Standards Board.
