Described as a “star in the making” since taking Silk in 2015, Duncan is much in demand for his advocacy and opinion in a broad spectrum of criminal and regulatory work, and in particular cases of homicide, terrorism, health and safety, and financial and corporate crime, both at first instance and in appellate proceedings.
As Treasury Counsel since 2009 and Senior Treasury Counsel since 2015, Duncan has appeared in numerous complex and high profile homicide cases, which in recent times have involved issues of contested medical causation, diminished responsibility and child-death. Duncan has a particular specialty in cases of gross negligence manslaughter, deaths in the context of health and safety regulation and deaths of persons in residential care or state detention.
Duncan has also appeared in numerous cases concerning allegations of terrorism, and relating to organised crime. In recent times, the latter has included the successful prosecution of the largest attempted importation of automatic weapons into the United Kingdom. Other cases in which he has also appeared as an advocate have involved allegations of rape, serious disorder, public nuisance, blackmail, prison escape, corruption, conspiracy to pervert the course of justice, and prosecutions under the Official Secrets Act.
Duncan also appears in cases of serious fraud and corruption, and has acted in both an advisory capacity and as an advocate for News UK, in the so called ‘hacking’ trials, for a UK FTSE company, and for senior executives in the international banking sector.
Duncan appears regularly in the Court of Appeal and in the Administrative Court, and has appeared on a number of occasions before the Judicial Committee of the House of Lords and latterly the Supreme Court.
In the Supreme Court these cases have addressed:
- the meaning of “terrorism” in the Terrorism Act 2000 (Gul ( UKSC 64),
- the ‘port stop’ provisions in Schedule 7 to Terrorism Act 2000 (Begal  UKSC 49)
- the DPP’s guidance in cases of assisted suicide (AM  UKSC 38),
- the requirement for causation in relation to road traffic related homicide (Taylor  UKSC 5)
- the re-evaluation of joint enterprise (Jogee  UKSC 8).
In the Court of Appeal and Administrative Court:
- Duncan appears regularly in application on behalf of the Attorney General to refer sentences as unduly lenient
- He appeared in guideline appeals concerning the interrelation of indeterminate sentences of imprisonment and the Mental Health Act 1983 (Vowles  EWCA Crim 45, fitness to plead (Marcantonio  EWCA Crim 14), the loss of control defence to murder (Gurpinar  EWCA Crim 178) and ), joint enterprise (Johson  EWCA Crim 1613)
- He has also appeared in a number of references of complex cases to the Court of Appeal by the Criminal Cases Review Commission, relating to circumstantial evidence (Wang Yam  EWCA Crim 1414), fresh material relating to witness credibility (Dorling  EWCA Crim 1750), and CCTV /identification issues (Robinson  EWCA Crim 923)
- He has appeared in challenges by judicial review to the ASBOs (Bulmer EWHC 2323 (Admin)) and the gang-related injunction provisions (James  EWCA Civ 552), and in relation to challenges to prosecutorial decisions.
Duncan has successfully acted in murder, manslaughter and attempted murder trials of all varieties, including cases of loss of control, self-defence, diminished responsibility, multi-handed ‘gang’ killings, juvenile defendants and cases with complex medical or other expert evidence. High-profile cases in his career have included the prosecution of Levi Bellfield for the murder of Milly Dowler, multiple homicide allegations against John Sweeney, and the murder for gain of Carole Waugh. Recent cases have included:
- Cases where the pathological evidence was limited or complicated due to the delayed recovery of the body or limited initial investigation, such as Gale and Trigg
- Cases involving extensive psychiatric evidence and the defence of diminished responsibility, such as Purcell, Samuels and Nandap
- A prosecution for corporate manslaughter (CAV Aerospace)
- Prosecution of gross negligence manslaughter through positional asphyxia during restraint (Wright)
- The prosecution of a number of individuals and companies relating to a death from gas inhalation (6699 Ltd.) and as a result of the falling of an unsecured window frame (West Green)
- A case relating to a 6 week old infant taken onto a bus by her mother in an attempt to conceal her death (Baker and Wiltshire)
Duncan also appeared in the Supreme Court when it reconsidered the liability of secondary parties in cases of murder (Jogee Gurpinar  EWCA Crim 178)), and in the Court of Appeal when the revised test was applied to six homicide cases (Johnson  EWCA Crim 1613).He also appeared when the Court of Appeal addressed the loss of control defence (Gurpinar  EWCA Crim 178).
Duncan has an extensive experience of involvement in the whole gamit of counter-terrorism prosecutions, having in the course of his career appeared as Leading, Junior and Sole Counsel in high profile terrorism- related cases, including the “fertiliser bomber” case (Khyam), which was then the largest joint operation of UK police forces, the security services and foreign law enforcement agencies and a large terrorist operation by the West Midlands Counter Terrorism Unit relating to a plot to kidnap a soldier (Khan). Recent cases have included:
- Allegation of preparation for acts of terrorism, involving persons accused of preparing to travel to Syria for the purposes of terrorism (Abdallah)
- Allegations of membership of a terrorist organization (Hamasallih)
- Allegations of preparation for acts of terrorism in the UK (Hussain)
Duncan has also acted as an adviser to the Government in relation to issues of disclosure in terrorism cases. He appeared in the Supreme Court to address the meaning of “terrorism” in the Terrorism Act 2000 in the case of Mohammed Gul ( UKSC 64), and in relation to the ‘port stop’ provisions of Schedule 7, Terrorism Act 2000 (Beghal  UKSC 49).
Health and Safety and Regulatory
Duncan has been instructed both in an advisory capacity and as an advocate in cases relating to breaches of Health and Safety and Environmental Protection legislation, both in criminal and inquest proceedings. In particular:
- Duncan has been instructed by the Office of Rail Regulation in relation to a number of serious rail accidents and rail-related fatalities,
- He has appeared as leading counsel in a health and safety related cases of Corporate Manslaughter
- He appeared in the prosecution of a number of individuals and companies relating to a death from gas inhalation (6699 Ltd.) and as a result of the falling of an unsecured window frame (West Green).
Fraud and Corporate Crime
Duncan has built up considerable experience in cases of serious and complex fraud and corruption, including cases involving the Serious Fraud Office, HMRC, the Financial Conduct Authority and the Department of Work and Pensions. He also has particular experience of Hi-Tech and computer-based fraud and other forms of “cybercrime” (see below), and in confiscation proceedings. Notable cases have included
- allegations relating to a substantial fraud against the NHS
- a substantial fraud relating to the Millennium Dome
- a substantial fraud alleged to have been committed by a bank employee through unprotected market speculation
- international corruption allegations involving activity in Saudi Arabia and Norway
Duncan has also in an advisory role for:
- A potential suspect in the SFO Libor investigation
- A high-profile individual in respect of investigations into alleged corporate and private misconduct as part of Operations Weeting and Elvedon
- A senior individual in the international banking sector
- A UK FTSE company facing investigation for alleged involvement in corruption
Duncan has been at the forefront of this developing area of criminal litigation. He acted from an early stage in an advisory capacity in Operation “Ore”, the international investigation of the incitement to supply indecent images of children. Other cases in this area have included Operation “Blossom”, a conspiracy to defraud the computer software industry with pirated software (the first large-scale prosecution by the National High-Tech Crime Unit) and the prosecution of fraud through the construction and distribution of malicious software.
Public and Administrative Law
Duncan is regularly instructed in relation to proceedings by way of judicial review, acting both in pre-action litigation and in the Administrative Court. Cases in which he has appeared have included:
- the acceptance by the Home Secretary and Serious Fraud Office of a letter of request from Italy in the context of fraud proceedings;
- the proper application of the Policing and Crime Act 2009 in relation to gang-violence injunctions
- challenges by judicial review to prosecutorial decisions, and applications relating to SFO/Police search warrant applications.
Inquests and Public Inquiries
Duncan has been instructed to act for interested parties in a number of inquests before the Coroner’s Court. These have included appearing both at the inquest and subsequent prosecution relating to the Potters Bar derailment, and the inquest relating to the death of a soldier at military barracks. Duncan appeared in an advisory capacity in the 7/7 inquest.
- Queen’s Counsel (2015)
- Recorder (2012)
- Treasury Counsel (2009) – Senior Treasury Counsel (2015)
- Editor, EU Law in Criminal Practice (Oxford University Press)
- Co-Author, Blackstone’s Guide to the Criminal Procedure Rules (Oxford University Press)
- Contributor, Fraud: Criminal Law and Procedure (Oxford University Press)
- Contributor, Blackstone’s Criminal Practice (Oxford University Press)
- University of Bristol (LLB Hons) (First Class)
- Lord Justice Holker Scholarship, Gray’s Inn