Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 127. Respect for Convictions and Religious Practices of Persons Deprived of Their Liberty
The UK Military Manual (1958) states:
Internees are to enjoy complete latitude in the exercise of their religious duties, provided that they comply with the disciplinary routine prescribed by the Detaining Powers. Ministers of religion when interned must be allowed to minister freely to the members of their community. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 63.
The manual further states that prisoners of war must be allowed complete freedom for the performance of their religious duties, and that adequate accommodation must be provided for religious services. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 156.
The UK LOAC Pamphlet (1981) provides: “Prisoners must be allowed freedom in the exercise of their religious beliefs. Accommodation must be provided for religious services.” 
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 8, p. 31, § 17(d).
The UK LOAC Manual (2004) states:
Internees are to enjoy complete latitude in the exercise of their religious duties, including attendance at services, provided that they comply with the disciplinary routine of the camp. Suitable accommodation for religious services must be provided. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 9.58.
On prisoners of war, the manual states:
Prisoners of war must be allowed complete freedom of religious worship, including attendance at services, provided that they comply with the disciplinary routine of the camp. Suitable accommodation for religious services must be provided. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 8.59.
With regard to internal armed conflicts in which the 1977 Additional Protocol II is applicable, the manual provides: “Internees or detainees … are entitled … to practise their religion and, if requested and appropriate, to receive spiritual assistance from chaplains or similar persons.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.40.
In 2004, in a reply to a question concerning detainees in Iraq, the UK Foreign and Commonwealth Office stated: “The prison conditions are in accordance with the Geneva Conventions … In order to accommodate religious practices, internees are served halal meat”. 
United Kingdom, Letter to the Clerk from the Parliamentary Relations and Devolution Department, Foreign and Commonwealth Office, 24 June 2004, published in House of Commons Foreign Affairs Committee, Foreign Policy Aspects of the War Against Terrorism: Seventh Report of the Session 2003–04, Vol. II: Oral and Written Evidence, HC 441-II.
In 2004, in a written answer to a question concerning “the document issued to service personnel announcing the ban on the use of hoods for Iraqi prisoners”, the UK Secretary of State for Defence stated:
An amended Standard Operating Instruction on the Policy for Apprehending, Handling and Processing Detainees and Internees was issued on 30 September 2003. The following section of the document contains the relevant information.
e. Food and water are to be provided as necessary, having regard to any national, ethnic or religious dietary requirements. 
United Kingdom, House of Commons, Written answer by the Secretary of State for Defence, Hansard, 7 July 2004, Vol. 423, Written Answers, col. 721W.
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:
12.18. … The personal convictions and religious practices of civilians of persons deprived of their liberty must be respected.
12.19. So, for example, the detainees in this case were entitled to halal food. 
United Kingdom, Ministry of Defence, Closing Submissions to the Baha Mousa Public Inquiry on Modules 1–3, 25 June 2010, §§ 12, 12.18 and 12.19, pp. 28 and 32.
[emphasis in original]