4.  Where an offence is alleged to have been committed on board any ship belonging to the German Democratic Republic by the master or a member of the crew, proceedings for the offence instituted otherwise than at the request or with the consent of a consular officer of the German Democratic Republic shall not be entertained by any court in the United Kingdom, unless—

(a) the offence is alleged to have been committed—

(i) by or against a person who is a citizen of the United Kingdom and Colonies, a British subject by virtue of sections 2, 13 or 16 of the British Nationality Act 1948 or the British Nationality Act 1965, or a British protected person within the meaning of the said Act of 1948; or

(ii) against a person other than the master or a member of the crew; or

(b) the offence is one involving the tranquillity or safety of the territory or territorial waters of the United Kingdom, or the law relating to safety of life at sea, public health, oil pollution, wireless telegraphy, immigration or customs; or

(c) the offence is one in respect of which the master of a ship belonging to the German Democratic Republic has given his consent to the institution of proceedings; or

(d) the offence is one punishable (on a first conviction) with imprisonment for a term that may extend to five years or with a more severe sentence.