Cleon Catsambis

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+44 (0)20 7832 1111

Cleon Catsambis has a broad and successful commercial practice that encompasses commercial litigation and dispute resolution, banking & financial services, fraud and regulatory & disciplinary law. He also practises in administrative and public law.

Cleon applies his commercial nous, robust legal analysis and strong advocacy skills to each of his cases in order to achieve the best possible outcome for his clients. He regularly appears as sole and junior counsel in high-value and complex disputes in the High Court, the Court of Appeal and a variety of Tribunals. He also undertakes pleading and advisory work.

He is an editor and contributing author to a number of publications, including Atkin’s Administrative Court Practice, Jordan’s Regulatory and Disciplinary Proceedings and Butterworths Financial Regulation Service.


Cleon undertakes pleading and advisory work and represents clients in all types of commercial cases, from simple contractual disputes to high-value complex multi-party litigation with an international dimension.

He has particular experience of banking & financial services, fraud and professional negligence claims, as well as applications for interim relief including freezing orders, search orders and general matters relating to disclosure and legal professional privilege.

Cleon’s cases often entail an international dimension, and he has experience of jurisdictions including the Russian Federation, Cyprus, the Netherlands, the Bahamas, the Cayman Islands and Jamaica.

Cleon accepts instructions in all types of commercial cases, including:

  • Tort and Contract Claims;
  • Banking and Financial services;
  • Professional negligence claims;
  • Commercial Fraud;
  • Shareholder disputes;
  • Procurement;
  • Intellectual Property (Copyright and Trademarks);
  • Agency;
  • International jurisdictional and forum disputes; and
  • Commercial ADR.

Notable experience includes:

  • Acting for Cornwall Council in successfully obtaining declaratory relief that it was entitled to lawfully terminate a 10-year £160m public procurement outsourcing contract forthwith on the basis of material breach (led by James Ramsden QC): BT Cornwall Ltd v Cornwall Council and others [2015] EWHC 3755 (Comm), [2015] All ER (D) 228 (Dec).
  • Defending contribution and negligence claims relating to an action under section 90 of the Financial Services and Markets Act 2000 for compensation for losses of c.£23m allegedly caused by misleading information in a rights issue prospectus (led by Andrew Tabachnik QC).
  • Advising, in respect of both domestic and international proceedings, on a US$200m claim involving allegations of ‘transactions at an undervalue’ and unlawful means conspiracy (with Hodge Malek QC).
  • Acting for a prominent Russian businessman in a US$60m Commercial Court claim involving complex issues of trust instrument interpretation, rectification, valuation and Russian and Cypriot law (led by James Ramsden QC).
  • Advising a committee of high-profile Premier League footballers and managers in a claim concerning the collusion of banks, accountants, independent financial advisers and agents in the mis-selling of financial products and investment schemes (with James Ramsden QC).
  • Advising a high net worth individual on a claim raising issues of state immunity and non-justiciability, misrepresentation, third party rights, collateral contracts and the assignability of arbitration clauses.

Cleon is a pro bono volunteer at the Bar Council’s CLIPS scheme of the Chancery Bar, as well as of the Queen’s Bench Division, advising and representing pro bono clients.

Banking & Finance

Cleon regularly advises and acts for firms, investors, banks and regulators on the full range of issues arising under the domestic and European/international legal framework, including compliance and enforcement, judicial review, professional negligence, mis-selling claims and collective investment schemes.

In 2014, Cleon worked in-house with the Enforcement and Financial Crime Division of the Financial Conduct Authority, concentrating on consumer credit issues. He advised the FCA on the interpretation and application of their statutory powers and considered the legal dimension of applications for authorisation.

Cleon was involved in the case of Conlon v Black Horse [2012] CTLC 193, which was ultimately determined by the Supreme Court in November 2014 (Plevin v Paragon Personal Finance Limited [2014] UKSC 61) and is the leading authority on the proper application of s.140A of the CCA 1974. On the back of that, Cleon has been involved in successful applications for permission to appeal based on the decision in Plevin and has advised both firms and individuals on the proper application of the unfair relationship regime.

Recent notable work includes:

  • Successfully representing the Financial Ombudsman Service in a significant judicial review challenge concerning its jurisdiction to review the manner in which an FCA review is conducted (as sole counsel).
  • Successfully overturning a proposed Prohibition Order against an individual accountant in the FCA’s Regulatory Decisions Committee (as sole counsel).
  • Advising in respect of a US$120m claim for breach of Directors’ duties in Cayman investment funds (with Hefin Rees QC).
  • Advising the minority shareholders of a Caribbean bank in respect of a derivative action and a petition for restraining oppressive action by the Directors and Managers of the bank (with Hefin Rees QC).
  • Advising on the proper application of the bank resolution provisions under Directive 2014/59/EU in the context of a major Cypriot banking dispute (with Hugh Mercer QC).

Cleon has had extensive involvement as a s.166 FSMA skilled person in a major review into the mis-selling of interest rate hedging products by two high-street UK banks.

Cleon is a contributing author to Butterworths Financial Regulation Service.

Regulatory & Disciplinary

Cleon has considerable experience in regulatory law, particularly in the financial services and healthcare sectors. He advises and acts for regulatory and professional bodies, government departments, firms and individuals. Cleon is a contributing author to the 8th edition of Jordan’s Regulatory and Disciplinary Proceedings (2015).

Financial Services

Cleon practices in all areas of financial services regulation. For further details please see the Banking & Financial Services section of his profile.


Cleon regularly advises and acts for most major regulatory bodies including the Health and Care Professions Council (having acted in over 30 High Court applications and appeals), the General Medical Council, the General Dental Council and the General Optical Council. Cleon was involved in the judicial review concerning the national reorganisation of paediatric cardiac surgery centres (R (Save our Surgery Ltd) v Joint Committee of Primary Care Trusts [2013] EWHC 439 (Admin)). In 2012, Cleon undertook a secondment at Monitor, the regulator for NHS Foundation Trusts. He also advises on the provider licence conditions, the enforcement regime and statutory interpretation.

Other regulatory experience

Cleon has also:

  • Advised and acted for the Solicitors Regulation Authority, particularly in respect of its powers to compel disclosure under s.44B of the Solicitors Act 1974;
  • Advised on the scope and mechanism for expanding reserved legal activities under the Legal Services Act 2007;
  • Advised a regulator as to whether its procedures breached Article 6 ECHR and/or Article 1 of the First Protocol;
  • Advised a regulator on the proper construction of its statutory remit as to sanctions; and
  • Assisted in Shell’s successful challenge to the OFT’s finding that it participated in price-fixing in the market for tobacco products contrary to domestic and EU law: Shell UK ltd v OFT [2012] Comp AR 61.


Cleon’s practice encompasses complex construction and infrastructure disputes. He has recently advised the UK government on a multi-million pound latent defects claim in respect of military facilities (as sole counsel). He has also acted in a high-value nuclear infrastructure dispute involving issues of delay and disruption, termination, professional negligence and contractual interpretation.

Administrative & Public

Cleon has a busy public law practice, encompassing civil liberties and human rights, immigration and asylum, education law, healthcare and mental health.

He is the Editor (with Hodge Malek QC and Saima Hanif) of Atkin’s Administrative Court Practice.

Cleon has extensive experience in judicial review proceedings and has been involved in the following notable cases:

  • Acting for the Financial Ombudsman Service in a challenge to its finding that it did not have jurisdiction to review the manner in which an FCA review is conducted (as sole counsel).
  • Challenging the Secretary of State for Communities and Local Government’s 2017 business rates revaluation transitional scheme, which concerns the business rate liability of hundreds of thousands of businesses across the country for the period 2017-2022 (led by Peter Village QC).
  • Acting for the Civil Aviation Authority (CAA) in a challenge concerning its duty to consult in respect of alterations to air traffic control patterns to Gatwick Airport (led by Gordon Nardell QC); and
  • Challenging the SFO’s refusal to permit legal representatives of choice at compulsory interviews pursuant to s.2(2) of the Criminal Justice Act 1987 (led by Jonathan Laidlaw QC): R. (Lord and Others) v Director of the Serious Fraud Office [2015] EWHC 865 (Admin).

Cleon’s experience further includes:

  • Advising Jamaica’s Independent Commission of Investigations on the exercise of its statutory functions, including the compellability of information (with Hodge Malek QC);
  • Advising County Councils on potential and actual legal challenges by service users and, among other things, the proper interpretation and application of the provisions of the Children Act 1989 and the Mental Health Act 1983;
  • Acting for a consortium of international media agencies in a challenge of the Enterprise and Regulatory Reform Bill which resulted in the Bill being amended (led by Richard Spearman QC); and
  • Advising on the prospects of obtaining an injunction to restrict protestors.

In matters of education law, Cleon regularly advises and represents schools, local authorities and parents on a wide range of issues including admissions appeals and infant class size appeals.

Cleon also assisted Jonathan Cooper OBE of Doughty Street Chambers in delivering the week-long Advanced Human Rights Law Training Programme for senior Foreign Office policymakers and diplomats.

Aviation & Aerospace

Cleon has a particular knowledge of and experience in the aviation sector. He regularly advises and acts for the Civil Aviation Authority, individual airports and airlines.

Cleon acted for the CAA in the judicial review proceedings concerning its duty to consult in respect of alterations to air traffic control patterns on the Westerly approach to Gatwick Airport (led by Gordon Nardell QC): R. (on the application of Barraud) v Civil Aviation Authority (Queen’s Bench Division (Administrative Court); 31 July 2015).

He has also advised the CAA in respect of airspace changes, consultation duties and post implementation reviews in respect of Gatwick Airport, London City Airport, Luton Airport and Edinburgh Airport.

Cleon has also advised multiple international airports on, among other things, the lawfulness of consultation exercises, environmental impacts and trials of new SIDs.

Cleon was involved in the litigation concerning Ryanair’s minority shareholding in Aer Lingus and whether it complied with EU and domestic merger regimes.

Call +44 (0)20 7832 1111 for more information

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