Sebastian practises as both leading junior and junior counsel in all aspects of serious crime. He is predominantly instructed in allegations of murder, armed robbery, large-scale importation and supply drugs offences and fraud, as well as prison work and inquests.

He has developed a particular expertise in offences under the Misuse of Drugs Act and has been involved some of the largest drugs cases in the UK.

Sebastian has a keen interest and expertise in issues surrounding the right to protest and to lawful assembly. He has provided advice on police powers and prosecutions for matters relating to civil disobedience and non-violent direct action.

He has successfully represented clients in the Court of Appeal and advises in that regard.

Called 1997.

Sebastian has lectured on various aspects of Misuse of Drugs Act 1971 for RELEASE and other organisations. He has also participated in in-house lectures on Criminal Procedures and Investigations Act 1996 and Criminal Justice Act 2003.