Year of call: 2011

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

Cleon applies his commercial nous, robust legal analysis and effective 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 leading publications, including Atkin’s Court Practice (Financial Services and Administrative Law volumes), Jordan’s Regulatory and Disciplinary Proceedings and Butterworths Financial Regulation Service. He also speaks regularly on issues ranging from legal professional privilege to consultation requirements.

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 injunctions, freezing orders, search orders and general matters relating to disclosure and legal professional privilege.

Cleon’s cases often involve 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:

  • Contract and Tort Claims;
  • Banking and Financial services;
  • Professional negligence claims;
  • Commercial Fraud;
  • Shareholder disputes;
  • Agency;
  • International jurisdictional and forum disputes; and
  • Commercial ADR.

Recent notable work includes:

  • 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).
  • Advising a major broadband and telecommunications provider in respect of a prospective benchmarking claim valued at £100m (as sole counsel).
  • Acting for the Claimant in respect of a £120m claim against a former director of a Cayman Islands investment manager to the Axiom Legal Financing Fund and her employer, the firm contracted to deliver governance services (with Hefin Rees QC).
  • 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 (with James Ramsden QC):  BT Cornwall Ltd v Cornwall Council and others [2015] EWHC 3755  (Comm).
  • Obtaining an injunction restraining the presentation of a winding-up petition relating to an undisputed debt on the basis of a genuine and serious multi-million pound cross-claim (as sole counsel): LDX International Group LLP v Misra Ventures Limited [2018] EWHC 275 (Ch).
  • Acting for a private collector in a dispute as to the ownership and provenance of a one-of-a-kind pre-Islamic jar valued at c.£12m (as sole counsel).
  • Advising a consortium 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).
  • Acting for a performance marketing company in a claim for unpaid commission in respect of crypto-currency web traffic generation (as sole counsel).
  • 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 (with James Ramsden QC).

Cleon also has experience of international arbitration, most recently advising in relation to a US$130m claim for breaches of a Shareholders and Noteholders Agreement in the Hong Kong International Arbitration Centre under UNCITRAL rules.

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.

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): R (on the application of Mazarona Properties Ltd) v Financial Ombudsman Service [2017] EWHC 1135 (Admin).
  • Successfully overturning a proposed Prohibition Order against a prominent accountant in the FCA’s Regulatory Decisions Committee (as sole counsel).
  • Advising a major Caribbean bank in respect of a US$300m claim against is former directors and senior managers for breaches of fiduciary duty and negligence (relating to mismanagement of the bank’s loan book and regulatory breaches) and against its former auditors for professional negligence (with Hefin Rees QC).
  • Advising on the proper application of the bank resolution provisions under Directive 2014/59/EU in the context of the Republic of Cyprus’ resolution of the Cypriot branch of FBME Bank Ltd on the basis of allegations of money laundering and funding of terrorism (with Hugh Mercer QC).
  • 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 (with Andrew Tabachnik QC).
  • Advising and acting in relation to claims of Unfair (Banking/Credit) Relationships under s.140A of the Consumer Credit Act 1974, having been involved in the leading case of Conlon v Black Horse  [2012] CTLC 193,  which was ultimately determined by the Supreme Court  in Plevin v Paragon Personal Finance Limited  [2014] UKSC 61.

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 an editor of Atkin’s on Financial Services (forthcoming 2018) and of Butterworths Financial Regulation Service (2014).

Cleon specialises in regulatory law, particularly in the financial services and healthcare sectors. He has considerable experience advising and acting for regulatory and professional bodies, government departments, firms and individuals.

Cleon is a contributing author to Jordan’s Regulatory and Disciplinary Proceedings (2017).

Financial Services

Cleon practises 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, the General Medical Council, the General Dental Council and the General Optical Council.

Cleon has extensive experience of statutory appeals to the High Court from the decision of healthcare regulators, see for example: Estephane v Health and Care Professions Council [2017] EWHC 2146 (Admin); Hall v Health and Care Professions Council (CO/17/2017); and  Falodi v Health and Care Professions Council  [2016] EWHC 328 (Admin).

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 advised 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 has a busy public law practice, encompassing judicial review, civil liberties and human rights, and 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): R (on the application of Mazarona Properties Ltd) v Financial Ombudsman Service [2017] EWHC 1135 (Admin).
  • 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 (with Peter Village QC).
  • Acting for the Civil Aviation Authority in a challenge concerning its duty to consult in respect of alterations to air traffic control patterns to Gatwick Airport (with 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  (with Jonathan Laidlaw QC):  R. (Lord and Others) v Director of the Serious Fraud Office [2015] EWHC 865 (Admin).

Cleon’s broader public law experience 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 a major Public Corporation in respect of proposed re-classification by the Office for National Statistics (with James Strachan QC);
  • Advising County Councils on potential and actual legal challenges by service users and, among otherthings, 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 (with Richard Spearman QC); and
  • Advising on the prospects of obtaining an injunction to restrict protestors.

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.

Cleon has a particular knowledge of and experience in the aviation sector. He regularly advises and acts for the Civil Aviation Authority (CAA), 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 (with 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.

2011: Bar Professional Training Course (Outstanding, Second in Year), BPP Law School

2010: Graduate Diploma in Law (Distinction), BPP Law School

2007: MSc Global Governance & Diplomacy (Distinction, First in Year), University of Oxford

2006: BSc  Government & History (First Class Honours), London  School of Economics

2015: Awarded a ‘red bag’ by James Ramsden QC “in recognition of an indispensable contribution to victory” in BT Cornwall Ltd v Cornwall Council and others  [2015] EWHC 3755  (Comm).

2012: Phoenicia Scholar (Bar European Group)

2011: Buchanan Prize (Lincoln’s Inn)

2010: Lord Denning Scholar (Lincoln’s Inn)

2010: Hardwicke Entrance Award (Lincoln’s Inn)

2009: Lord Bowen Scholar (Lincoln’s Inn)

Editor, Atkin’s Financial Services Court Practice (forthcoming, 2018)  with Hodge Malek QC et al

Contributing author, Jordan’s Regulatory and Disciplinary Proceedings (9th  ed) (2017)

Editor, Atkin’s Administrative Court  Practice (2016)  with Hodge Malek QC and Saima Hanif

Contributing author, Butterworths Financial Regulation Service (2014)

Eleanor Gray QC and Cleon Catsambis, “2012: A Year in Judicial Review”, Judicial Review  Volume 18, Issue 1, 2013