Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 146. Reprisals against Protected Persons
Section C. Medical and religious personnel in the power of the adversary
The UK Military Manual (1958), in a footnote relating to a provision which refers to Articles 14 and 46 of the 1949 Geneva Convention I and Articles 16 and 47 of the 1949 Geneva Convention II, notes: “Reprisals are unlawful against all persons except enemy combatants and those few classes of civilians who are not protected persons.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 644, footnote 2.
The UK LOAC Pamphlet (1981) provides: “The [1949] Geneva Conventions and [the 1977 Additional Protocol I] prohibit reprisals against … medical and religious personnel”. 
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 4, p. 17, § 16.
The UK LOAC Manual (2004) states: “Reprisals are never lawful if directed against any of the following: a. … medical personnel and chaplains, medical units, establishments and transports”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.18.
In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United Kingdom stated:
To be lawful, a belligerent reprisal must meet two conditions. First, it must not be directed against persons or objects against which the taking of reprisals is specifically prohibited … The Geneva Conventions of 1949 prohibit the taking of reprisals against persons or objects protected by the Conventions. 
United Kingdom, Written statement submitted to the ICJ, Nuclear Weapons case, 16 June 1995, pp. 58–59.
Upon ratification of the 1977 Additional Protocol I, the United Kingdom stated that in the event of violations of Articles 51–55 of the 1977 Additional Protocol I by the adversary, the United Kingdom would regard itself entitled to take measures otherwise prohibited by these Articles, noting, however, that: “Any measures thus taken by the United Kingdom … will not involve any action prohibited by the Geneva Conventions of 1949.” 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § (m).