Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 65. Perfidy
Section G. Simulation of protected status by using the United Nations emblem or uniform
According to the UK LOAC Manual (2004), “the feigning of protected status by the use of signs, emblems or uniforms of the United Nations” is an example of prohibited perfidy, “if done with intent to betray the enemy’s confidence”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.9.2.
In its chapter on maritime warfare, the manual states that launching an attack while feigning protected United Nations status is an example of perfidy. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 13.83.
In its chapter on the application of the law of armed conflict during peace-support operations, the manual states:
The parties to an armed conflict are prohibited to make use of the emblem of the United Nations except as authorized by the United Nations. In addition, it is prohibited to kill, injure or capture an adversary by feigning protected status by the use of signs, emblems or uniforms of the United Nations and to do so constitutes the war crime of perfidy. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 14.13.
The UK Geneva Conventions Act (1957), as amended in 1995, punishes “any person, whatever his nationality, who, whether in or outside the United Kingdom, commits, or aids, abets or procures the commission by any other person of, a grave breach of … [the 1977 Additional Protocol I]”. 
United Kingdom, Geneva Conventions Act, 1957, as amended in 1995, Section 1(1).
Under the UK ICC Act (2001), it is a punishable offence to commit a war crime as defined in Article 8(2)(b)(vii) of the 1998 ICC Statute. 
United Kingdom, ICC Act, 2001, Sections 50(1) and 51(1) (England and Wales) and Section 58(1) (Northern Ireland).