Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 87. Humane Treatment
Section A. General
The UK LOAC Pamphlet (1981) states that “in the event of a civil war, Common Article 3 to the 1949 Geneva Conventions provides: a. that persons out of the fighting … because they are wounded … must be treated humanely”, notably they “may not be subjected to any form of violence”. 
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 12, p. 42, § 2.
The UK LOAC Manual (2004) states:
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”. Their persons, honour, convictions and religious practices must be respected. 
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.
The UK Armed Forces Act (2006) provides: “A person subject to service law commits an offence if … he ill-treats a person who is on board a ship or aircraft when it is taken as prize.” 
United Kingdom, Armed Forces Act (2006), Section 38.
In 2010, in its closing submissions to the public inquiry into the circumstances surrounding the death of Baha Mousa and the treatment of those detained with him by UK armed forces in Iraq in 2003, the UK Ministry of Defence stated regarding common Article 3 of the 1949 Geneva Conventions: “On its face this protection is restricted to armed conflicts not of an international character. However, it is understood to apply in all forms of armed conflict as part of customary international law to set out the irreducible minimum standard.” 
United Kingdom, Ministry of Defence, Closing Submissions to the Baha Mousa Public Inquiry on Modules 1–3, 25 June 2010, § 10.2, p. 10.
The Ministry of Defence further stated:
12. The treaties setting out rules of IHL are supplemented by rules of customary international law (CIL), i.e. rules which are recognized as binding by States, even though they do not appear in treaty texts. … [I]n relation to the rules described below the Government accepts that they reflect CIL. It is suggested that the rules which are of most relevance to this inquiry are:
12.3. … Civilians and persons hors de combat must be treated humanely. 
United Kingdom, Ministry of Defence, Closing Submissions to the Baha Mousa Public Inquiry on Modules 1–3, 25 June 2010, §§ 12 and 12.3, p. 28.
[emphasis in original]