Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 88. Non-Discrimination
Section C. Wounded and sick
The UK Military Manual (1958) states that the wounded and sick “must be cared for … without adverse distinction based on sex, race, nationality, religion, political belief or any other similar test”. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 339.
The UK LOAC Pamphlet (1981) provides that, in the event of a civil war, “persons out of the fighting … because they are wounded must be treated … without any adverse discrimination”. 
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(a).
The UK LOAC Manual (2004) states:
7.3. The wounded and sick are to be protected and respected. …
7.3.1. The duty of respect means that the wounded and sick are not to be made the target of attack. The duty of protection imposes positive duties to assist them. The Geneva Conventions and Additional Protocol I do not seek the unattainable by what would be a vain attempt at removing all hardships arising from armed conflict affecting the groups of persons defined above; they merely seek to ameliorate their conditions. They expressly do so “without any adverse distinction founded on 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”.
7.3.2. Paragraph 7.3 applies to all wounded and sick, whether United Kingdom, allied or enemy, military or civilian. They are entitled to respect and protection [and] humane treatment. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 7.3–7.3.2.
With regard to priority of treatment, the manual states:
There must be no discrimination on grounds of sex, race, nationality, religion, political belief or any other similar test. Spies, saboteurs, partisans and illegal combatants who are wounded or sick are entitled to the same treatment. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 7.3, footnote 4.
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.
In its chapter on enforcement of the law of armed conflict, the manual states:
States are under a general obligation to issue orders and instructions requiring compliance with the law of armed conflict and to take steps to see that those orders and instructions are observed. There is a specific provision in relation to the handling of the wounded, sick and shipwrecked, extending to a requirement to provide for unforeseen situations “in conformity with the general principles” of the Geneva Conventions 1949. These are that the wounded, sick and shipwrecked should be cared for and treated without any adverse distinction. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.2.