A good start would be by revoking this Jihadist's British Citizenship should the allegations be proven well grounded.

Or;

Quote:

In English law, where murder and manslaughter are concerned, the English court has jurisdiction over offences committed abroad, if it was committed by a British citizen (see section 9 of the Offences against the Person Act 1861 and section 3 of the British Nationality Act 1948). http://en.wikipedia.org/wiki/Crimina...ction#Problems

Or; Apprehend and arrest him and deliver him to the US military authorities. Gitmo is waiting for his ass. A criminal trial in the Federal Courts for indictment of capital murder is also possible.

Other protected persons: humanitarian workers, journalists, medical and religious personnel
International Red Cross:
http://www.icrc.org/eng/war-and-law/...ed-persons.htm

Quote:

18 U.S.C.1116 (killing an internationally protected person) Jurisdictional factors: - the victim was a United States national; - the offender was a United States national; or - the offender is afterwards found in the United States http://fas.org/sgp/crs/misc/94-166.pdf via Federation of American Scientists reproduced from; Congressional Research Service 7-5700 crs.gov