Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 91. Corporal Punishment
The UK Military Manual (1958) prohibits measures against protected persons which will cause physical suffering and states: “This prohibition applies … to corporal punishments.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 42.
The manual further states: “Corporal punishments … are forbidden.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 205.
The manual states that, in occupied territories, the prohibition of measures of such character as to cause the physical suffering or extermination of protected persons in the hands of the occupant “applies … to corporal punishment”. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 549.
The manual recalls that “corporal punishment is excluded” with regard to the punishment of war criminals. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 638.
The UK LOAC Pamphlet (1981) forbids corporal punishment. 
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: “Corporal punishment and cruelty in any form are prohibited.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.48; see also §§ 9.4 (civilians in the hands of a party to the conflict) and 8.121 (prisoners of war).
With regard to internal armed conflicts in which the 1977 Additional Protocol II is applicable, the manual provides:
The following acts against protected persons “are and shall remain prohibited at any time and in any place whatsoever”. These are:
a. … any form of corporal punishment. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.38.
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:
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:
12.10. … Corporal punishment is prohibited.
12.11. Accordingly, even had the imposition of the stress positions to which the detainees were subjected been legal (which it was not) then punishing them with violence for failing to maintain them was contrary to IHL. 
United Kingdom, Ministry of Defence, Closing Submissions to the Baha Mousa Public Inquiry on Modules 1–3, 25 June 2010, §§ 12, 12.10 and 12.11, pp. 28 and 30–31.
[emphasis in original]