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Gwion Lewis

Year of call: 2005

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Practice Summary

Gwion Lewis was called to the Bar of England & Wales in 2005. "A top-class advocate" (Legal 500, 2015) and a former US-UK Fulbright Scholar specializing in international human rights, Gwion has extensive experience of litigation and advisory work in public international law. He has particular expertise in the areas of human trafficking, asylum and human rights, international environmental law and the international law of the sea, but welcomes instructions in all areas of public international work.

Gwion is also one of the UK’s leading experts on the international law relating to regional and minority languages, having authored the leading text on the law relating to the Welsh language (Hawl i’r Gymraeg). He is regularly instructed by governments, regulators and NGOs to advise on legal reform relating to minority language issues.

Gwion is a member of the Attorney General's 'A' Panel of Junior Counsel, which means that he regularly acts for the UK Government in its most complex cases. He is also a member of the Welsh Government's Panel of Junior Counsel. He is recommended as a leading junior in the main independent legal directories. Recent comments in Chambers & Partners UK include:

  • Administrative & public law (2016): “The extent of the detail and the effort he puts in is fantastic. The turnaround of his work is excellent.” “He’s approachable, goes the extra mile and gives one prompt and thorough service with speed and accuracy.”

  • Administrative & public law (2015): “His pleadings are extremely effective.” “He is adept at assimilating large amounts of information and separating the wheat from the chaff. He has a good manner with clients, listens to what others say and is a fearsome cross-examiner.”

  • Planning law (2016): “In terms of turnaround of work and service levels, he is excellent.” “He is an intelligent and able barrister and is easy to deal with.”

Details of his recent and ongoing international work are set out below.

Human trafficking

Gwion appears regularly in litigation relating to the Council of Europe Convention on Action against Trafficking in Human Beings. He acted for the Secretary of State in the first case in the UK on the scope of the obligation to take “protective” measures, pursuant to Article 4 ECHR, in the face of an alleged “real and immediate” risk of re-trafficking: R (TDT) v Secretary of State for the Home Department (CO/5432/2015). He is also acting for the Secretary of State in a forthcoming case in the Court of Appeal that will determine the jurisdiction, if any, of the First-Tier and Upper Tribunals in the UK to review decisions made by the Home Office under the Anti-Trafficking Convention: R (MS (Pakistan)) v Secretary of State for the Home Department (AA/07855/2013).

Gwion has trained several public bodies on their obligations under the Anti-Trafficking Convention and speaks frequently about the subject in the media. 

Asylum and human rights

Gwion has a long-standing interest in this area, having focused on international human rights law whilst studying for the LLM in New York University and the BCL at the University of Oxford. This has led to asylum and human rights law becoming a major part of Gwion’s practice. Recent highlights include:

  • R (Khan) v SSHD [2016] EWCA Civ 416 – leading authority on the duty of candour when seeking to challenge immigration decisions.

  • R (Onykwere) v SSHD [2016] EWHC 758 (Admin) – whether the relationship of a Cameroon national with his British-born son had improved sufficiently to grant him a fresh Article 8 claim.

  • R (WT) v SSHD [2016] EWHC 659 (Admin) – challenge to the lawfulness of detaining a Burmese national pending his deportation.

  • R (Hasmi) v SSHD [2014] EWHC 14 (Admin) – challenge to the refusal to grant indefinite leave to remain to an Afghan national who was in the ‘legacy’ of unresolved cases.

  • R (AA (Sudan)) v SSHD [2014] EWHC 2118 (Admin) – whether a father’s outstanding application for contact with his child in family law proceedings meant that he could no longer be lawfully detained.

  • Tsavdaris v Home Office [2014] EWHC 440 (QB) – effect of the transitional provisions of the Immigration (EEA) Regulations 2006 on the lawfulness of detention.

  • R (Al-Beri) v SSHD (2014, settled) – judicial review of the alleged failure of the SSHD to make adequate arrangements to process applications for family reunion by those affected by hostilities in Syria.

  • R (Kajuga) v SSHD [2014] EWHC 426 (Admin) – judicial review of the 2 year detention of a person claiming to be from Burundi, but unable to prove it.

  • R (Mahlu) v SSHD [2012] EWHC 2623 (Admin) – whether an Eritrean national could be lawfully removed to Italy pursuant to the Dublin II Regulation.

  • R (Capital Care Services UK Ltd) v SSHD [2012] EWCA Civ 1151 – challenge to the revocation of a licence to sponsor migrants under Tier 2 of the points-based system.

Gwion also has considerable experience of litigation and advisory work relating to the right to the peaceful enjoyment of possessions under Article 1 of the First Protocol to the ECHR (“A1P1”). Recent/ongoing cases in this area include:

  • R (Mott) v Environment Agency [2015] EWHC 314 (Admin) (appeal outstanding) – resisting an A1P1 challenge to the Agency’s decisions to set low catch allocations for salmon fishing in the River Wye.

  • King and others v Environment Agency (High Court, ongoing) – claim for A1P1 damages based on flood management measures taken by the Agency in Gloucestershire. 

International environmental law

Gwion advises on all aspects of international environmental law. In the last five years, Gwion has acted for Natural Resources Wales (and its predecessor, Environment Agency Wales) in all its environmental litigation in the higher courts, with international environmental law featuring prominently in all cases. He also regularly advises the most respected environmental NGOs, including WWF UK, ClientEarth and Friends of the Earth. In 2014, he accepted an invitation by the Government of South Korea to address its officials in Paris on emerging developments in international environmental law.

Other recent highlights in this area include:

  • R (Seiont, Gwyrfai and Llyfni Anglers’ Society) v Natural Resources Wales [2015] EWHC 3478 (Admin) (appeal outstanding) – acting for NRW in the first case to challenge the transposition of the Environmental Liability Directive in the UK (with David Forsdick QC).

  • Tidal Lagoon Swansea Bay (2014): acted for NRW throughout the 3-week examination of whether development consent should be given for the world’s first man-made, energy-generating tidal lagoon, a case raising difficult novel questions under the Water Framework Directive.

  • Acting for the Environment Agency in several appeals against its decisions to issue penalty notices under (i) the Greenhouse Gas Emissions Trading Scheme Regulations; and (ii) the CRC Energy Efficiency Scheme Order (ongoing since 2012).

  • Advising NRW in relation to the coal-fired operations at Aberthaw power station and their compliance with the Large Combustion Plant Directive.

  • Advising the Welsh Ministers on the transposition of the Marine Strategy Framework Directive.

  • R (Repic Ltd) v Secretary of State for Business, Enterprise and Regulatory Reform [2009] EWHC 2015 – representing the Secretary of State in a challenge to the UK’s transposition of the Waste Electrical and Electronic Equipment (WEEE) Directive (with David Elvin QC).

International language law

As a native speaker of Welsh, Gwion has a keen interest in the law relating to the protection and promotion of regional and minority languages. His first book, Hawl i’r Gymraeg (The Right to Welsh), was the first to provide in-depth analysis of language rights in EU and international law in the Welsh language. In February 2014, when acting for the Welsh Language Commissioner, Gwion broke new ground by using the Welsh language when making submissions to the High Court of England and Wales, the first time that this had happened since the court was established in 1875.

Gwion is regularly instructed to advise governments, regulators and NGOs on issues arising under the European Charter for Regional and Minority Languages. He also has extensive experience of advising on language rights issues under the ECHR, particularly in the context of Article 10 (freedom of expression) and Article 2 of the First Protocol (right to education). Recent consultancy work has given Gwion particular knowledge of language issues in the Nordic countries and in Ukraine. 


Gwion is Welsh-English bilingual, has good French and is a certified upper-intermediate (B2) Italian speaker (University of Siena, CILS).