Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 88. Non-Discrimination
Section B. Civilians
The UK Military Manual (1958) prohibits discrimination in the treatment of protected civilians and stipulates that non-discrimination also applies in occupied territories. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, §§ 39, 133 and 547.
The UK LOAC Pamphlet (1981) prohibits discrimination in the treatment of protected civilians. 
United Kingdom, The Law of Armed Conflict, D/DAT/13/35/66, Army Code 71130 (Revised 1981), Ministry of Defence, prepared under the Direction of The Chief of the General Staff, 1981, Section 9, p. 35, § 9.
The UK LOAC Manual (2004) states n its chapter on the protection of civilians in the hands of a party to the conflict:
All persons are to be treated humanely in all circumstances and “without any adverse distinction based upon race, colour, sex, language, religion or belief, political or other opinion, national or social origin, wealth, birth or other status or on any other similar criteria”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 9.3.
In its chapter on internal armed conflict, the manual restates the provisions of common Article 3 of the 1949 Geneva Conventions:
Under the terms of Common Article 3, the parties to a non-international armed conflict occurring in the territory of a party to the Conventions are obliged to apply “as a minimum”, the following provisions:
(1) Persons taking no active part in the hostilities, including members of armed forces who have laid down their arms and those placed hors de combat by sickness, wounds, detention, or any other cause, shall in all circumstances be treated humanely, without any adverse distinction founded on race, colour, religion or faith, sex, birth or wealth, or any other similar criteria. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.4.