Sebastian Walker

Sebastian has particular experience in serious and complex crime having been instructed as junior alone in cases of serious violence (including s.18 and kidnap), firearms offences and international class A drugs conspiracies. Sebastian also acts regularly as a led junior in paper heavy, multi-defendant matters.

Recent instructions include:

• Op K [2026] – led junior for the Crown in the prosecution of 24 defendants for a large scale cocaine conspiracy across the East Midlands.
• Op W [2026] – junior alone for the CCU prosecuting six defendants for “hub and spoke” conspiracies to supply kilograms of cocaine and heroin.
• R v CF [2025-26] – leading junior for the defence in a conspiracy to commit robbery relating to five professionally planned armed robberies of betting shops in East London. The case was heard over three trials lasting 23 weeks, with one jury discharged and the second hung after 40 days.
• R v D [2025] – junior alone for the defence in a SEOCID prosecution under the Serious Crime Act 2007 for D’s involvement as a moderator of a dark web drugs site and related movement of large amounts of Bitcoin.
• R v S [2025] –junior alone for the CCU prosecuting two separate indictments relating to an acid attack that took place against a background of drug debt (charged contrary to s.29 of the OAPA 1861), and the subsequent discovery of a large number of explosive items (including a quantity of HMTD) created by the attacker.

Sebastian has a keen interest in financial crime proceedings and has been instructed as junior alone and led junior in a number of fraud, money laundering and computer misuse cases. He has particular expertise dealing with cases involving cryptocurrency and the layering of transactions as well as

Recent instructions include:

• Op A [ongoing] – led junior in the prosecution of three defendants for the laundering of over £20 million in gold bars. The case involves extensive evidence as to the attribution of shell companies, detailed examination of seized business documents and involves investigation into businesses in Belgium, Dubai, Pakistan and Turkey. Gold and money laundering experts both instructed.
• Op S [ongoing] – junior alone in the prosecution of four defendants for a cryptocurrency account takeover committed against victims in the United States of America and related money laundering offences.
• Op T [ongoing] – led junior in the prosecution of three Vietnamese defendants for various international money laundering offences, including the use of airline staff to smuggle quantities of cash.
• Op E [2026] – led junior for first of five defendants in a multi-million money laundering conspiracy involving in excess of 80,000 pages (surveillance, phones and banking material). The case involved contested money laundering expert evidence and the role of legitimate Hawala banking. Sebastian conducted the lead cross-examination of the NCA money laundering expert.

Sebastian is a member of the SFO proceed of crime panel at level B, and the CPS specialist proceeds of crime panel at level 3. He acts at all stages of proceeds of crime proceedings – investigatory, post-conviction and civil. He has acted in proceedings involving restraint orders, freezing orders and continued detention of assets, including in respect of millions of pounds of assets. He has authored articles in both the Criminal Law Review and Archbold Review on confiscation. He appears for defendants and prosecuting and investigating authorities (including HMRC and police forces)

He has experience of dealing with complex issues at confiscation including hidden assets, cryptocurrency valuations and abuse of process.

Recent instructions include:

• R v D [2026] – junior alone for the defence following conviction for various cryptocurrency money laundering offences. Issues included valuation of changing assets; cryptocurrency tracing; and third party interests.
• Op D [2026] – junior alone in relation to confiscation proceedings against four defendants following convictions for Encrochat organised drug supply. Case involved issues relating to abuse of process; challenges to benefit in the context of couriers; and third party interests.
• Op T [2025 – 2026] – junior alone for confiscation proceedings relating to conspiracies to burgle involving £3.5 million tiara and numerous high value watches. Issues included relationship with compensation; hidden assets abroad; accountancy expert evidence; and changes in value of foreign currency.

Sebastian accepts instructions in private prosecutions of all types. In addition to his experience prosecuting cases on behalf of the CPS he has experience of prosecuting and defending in cases brought by private prosecutors. He has prosecuted on behalf of individuals, local authorities and the Insolvency Service. He is familiar with the issues that arise in non-paper cases and has a particular eye for the disclosure issues that often result.

Sebastian is a member of the CPS specialist panel for Counter-Terrorism at level 3. He has appeared in a variety of cases, including cases raising human rights arguments and abuse of process issues.

Sebastian accepts instructions in relation to crime-related public law proceedings. He has acted in a number of prison law cases involving prisoners convicted of terrorism offences; was second junior to Duncan Atkinson KC in the Post Office Horizon Inquiry (who gave expert evidence on decision making in the criminal investigations and prosecutions); and has advised on issues including transfer of prisoner agreements.

Sebastian holds the following editorial appointments:

• Contributing Editor – Archbold Criminal Pleading, Evidence and Practice (since January 2019)
• Co-Editor – Current Sentencing Practice (since March 2020)
• Co-Editor – Criminal Appeal Reports (Sentencing) (since March 2020)
• Co-Author – Sentencing Principles, Procedure and Practice (since April 2020)
• Editorial Board Member – Criminal Law Week (since September 2021)
• Co-Editor – Lloyd’s Law Reports: Financial Crime (since December 2024)

He has been published in the Criminal Law Review, Archbold Review, the Law Quarterly Review, Public Law and Sentencing News on topics as varied as confiscation, mutual legal recognition, historic sentencing, challenges to Encrochat evidence and the presentation of evidence in paper heavy cases.

Before coming to the Bar Sebastian worked at the Law Commission (instructing Parliamentary Counsel on the drafting of the Sentencing Act 2020) and the Attorney General’s Office (advising on consent applications, contempt of court matters and unduly lenient sentences).

He also taught law at the University of Cambridge and the London School of Economics.

CPS Panel Advocate, Level 3 (general crime; serious crime; counter terrorism, fraud and POCA)

SFO Panel Advocate, B Panel (fraud and POCA)

Member, Criminal Bar Association (and committee member of the Education Committee)

BA (Hons) Law (University of Nottingham)

LLM in Criminal Justice (University of Nottingham)

Bar Professional Training Course (The City Law School)