The United Nations Personnel Act 1997 is entitled "An Act to enable effect to be given to certain provisions of the Convention on the Safety of United Nations and Associated Personnel adopted by the General Assembly of the United Nations on 9th December 1994".
This is regardless of the nationality of the offender and regardless of whether he knows that other person is a UN worker (United Nations Personnel Act 1997 s.5).
Extradition rules cover offences under the 1997 Act (see s.6). Proceedings require consent of the Attorney General (s.5(1)).