Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 128. Release and Return of Persons Deprived of Their Liberty
The UK Military Manual (1958) states: “Prisoners of war must be released and repatriated without delay after the cessation of active hostilities.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 261.
The UK LOAC Pamphlet (1981) provides: “PW [prisoners of war] must be released and repatriated without delay after the cessation of active hostilities.” 
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. 33, § 22.
The UK LOAC Manual (2004) states:
Prisoners of war must be released and repatriated without delay after the cessation of active hostilities. The detailed arrangements should be included in an armistice agreement. However, if they are not, each of the detaining powers must quickly prepare and implement a repatriation scheme … The duty of repatriation is absolute and may not be made conditional upon the behaviour of the state on which the prisoners depend. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 8.168.
In its chapter on enforcement of the law of armed conflict, the manual notes:
Additional Protocol I extends the definition of grave breaches to include the following:
c. the following, when committed wilfully and in violation of the Conventions or the protocol:
(2) unjustifiable delay in the repatriation of prisoners of war or civilians. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.25(c)(2).
The UK Geneva Conventions Act (1957), as amended in 1995, punishes “any person, whatever his nationality, who, whether in or outside the United Kingdom, commits, or aids, abets or procures the commission by any other person of, a grave breach of … [the 1977 Additional Protocol I]”. 
United Kingdom, Geneva Conventions Act, 1957, as amended in 1995, Section 1(1).
In 2003, the following question was addressed to the UK Government in the House of Lords:
(a) why, more than a year after the end of major fighting, the nine British citizens held at Guantanamo (Cuba) and Bagram (Afghanistan) have not been either charged or released;
(b) whether their future depends solely on the United States Government;
(c) if so, why; and
(d) whether it was correctly reported in some editions of The Times of 3 February that British officials warned the men that there is little that Her Majesty’s Government can do to secure their release, despite their having answered intelligence questions. 
United Kingdom, House of Lords, Written question by a Member, Hansard, 18 February 2003, Vol. 644, Written Answers, col. WA167.
In a written reply, the UK Parliamentary Under-Secretary of State, Foreign and Commonwealth Office, stated:
The US has said that the detainees are enemy combatants captured in a continuing armed conflict and held in that capacity by the US military authorities. The question of the status of the detainees at Guantanamo Bay under international humanitarian law has to be considered in the light of the facts relating to each individual detainee.
We remain in regular contact with the United States, at both ministerial and official level, about the situation of the detainees. My right honourable friend the Foreign Secretary has raised the issue several times with US Secretary of State Colin Powell, most recently on 23 January. We have been encouraging the US to move forward with the process of determining the future of the British detainees. We shall continue to do so.
The discussions between British officials and the detainees are confidential as they contain personal information about the detainees. I am withholding further details of the visits by British officials to the detainees at Guantanamo Bay under exemption 1a of the Code of Practice on Access to Government Information, (information whose disclosure would harm national security or defence). 
United Kingdom, House of Lords, Written answer by the Parliamentary Under-Secretary of State, Foreign and Commonwealth Office, Hansard, 18 February 2003, Vol. 644, Written Answers, col. WA167.
In 2003, in a written reply to a question in the House of Commons, the UK Parliamentary Under-Secretary of State, Foreign and Commonwealth Office (FCO), stated:
FCO officials and I call regularly upon the parties to the Western Sahara dispute to take action on human rights issues. In February this year, I called for the immediate release of the remaining 1,160 Moroccan prisoners of war held by the Polisario Front, some held for over 25 years and some are in poor physical and mental health. 
United Kingdom, House of Commons, Written answer by the Parliamentary Under-Secretary of State, Foreign and Commonwealth Office, Hansard, 28 April 2003, Vol. 404, Written Answers, col. 134W.
In 2003, in a written reply to questions in the House of Lords, the UK Parliamentary Under-Secretary of State for Defence, Lord Bach, stated:
Lord Oakeshott of Seagrove Bay asked Her Majesty’s Government:
Further to the Written Answer by the Lord Bach on 30 June (WA 64), how many people captured by British forces in Iraq and transferred to United States internment facilities have neither been released nor classified as prisoners of war.
Lord Bach: As of 3 July 2003, the United States is holding one prisoner of war and 22 other persons captured by British forces, who are either suspected of committing criminal offences or are interned where necessary for imperative reasons of security in accordance with the Fourth Geneva Convention. All other British captured prisoners of war have been released under the supervision of British forces, and with the knowledge of the International Committee of the Red Cross.
Lord Oakeshott of Seagrove Bay asked Her Majesty’s Government:
What assurances they have received from the United States authorities about the treatment of people captured by British forces in Iraq and transferred to United States internment facilities; whether any of them could face the death penalty; and when they will be released or tried.
Lord Bach: The United Kingdom of Great Britain and Northern Ireland’s and United States’ responsibilities in relation to captured persons are contained in an arrangement between the nations. In accordance with this arrangement, the United States agreed to treat persons in accordance with the relevant Geneva Conventions. Under the terms of the arrangement, the United Kingdom of Great Britain and Northern Ireland has primary right to criminal jurisdiction for offences committed prior to transfer. For offences committed after transfer, the United States has primary right to jurisdiction, and in such cases it is up to the United States to decide sentence. We are not aware of any situation where United Kingdom of Great Britain and Northern Ireland captured persons have committed any post transfer offences. In the absence of any post transfer offences, the decision to release rests with the United Kingdom of Great Britain and Northern Ireland authorities.
Persons suspected of crimes other than against coalition forces or the security of Iraq are immediately handed over to Iraqi authorities. Persons suspected of crimes against coalition forces or the security of Iraq are held pending collection of evidence and a decision as to the forum for trial. Persons held for imperative reasons of security, in accordance with the Fourth Geneva Convention, will be released as soon as their internment ceases to be necessary. 
United Kingdom, House of Lords, Written answers by the Parliamentary Under-Secretary of State for Defence, Hansard, 8 July 2003, Vol. 651, Written Answers, cols. WA31–WA32.
In 2003, in a written reply to a question in the House of Lords, the UK Parliamentary Under-Secretary of State for Defence, Lord Bach, stated:
Lord Oakeshott of Seagrove Bay asked Her Majesty’s Government:
Further to the Written Answer by the Lord Bach on 16 July (WA125), for how much longer they expect to keep without trial the 71 persons captured by British forces interned for imperative reasons of security; and how and by whom they expect the prisoners to be tried if they are not released.
Lord Bach: Of the 71 persons held for imperative reasons of security on 15 July, 49 have already been released. The remainder will be held until it is assessed that their internment is no longer necessary for reasons of security, all cases are subject to regular review. In cases where there is evidence to suggest that a criminal offence has been committed, persons captured by United Kingdom of Great Britain and Northern Ireland forces are handed to the Iraqi judicial system. If internment is based on intelligence material that justifies internment, the case will not be suitable for trial, although cases will be subject to regular review. 
United Kingdom, House of Lords, Written answer by the Parliamentary Under-Secretary of State for Defence, Hansard, 8 September 2003, Vol. 652, Written Answers, col. WA45.
In 2003, in a written reply to a question in the House of Commons, the UK Minister of State for the Armed Forces, Ministry of Defence, stated:
Article 78 of the IV Geneva Convention (1949) allows the UK as the Occupying Power to intern people where it considers it necessary for reasons of security. Internees will continue to be held until such time as they are no longer considered a threat to Coalition Forces. A review is conducted at the 10, 28 and 90 day points (and every 90 days thereafter) to determine whether continued internment is necessary. Internees enjoy all their rights under the Geneva Conventions.
As at 1 December, all internees held by the UK Forces in Iraq are of either Iraqi or Sudanese nationality. 
United Kingdom, House of Commons, Written answer by the Minister of State for the Armed Forces, Ministry of Defence, Hansard, 8 December 2003, Vol. 415, Written Answers, col. 269W.
In 2004, in a reply to a question concerning the status of detainees in Iraq, the UK Foreign and Commonwealth Office stated:
The legal basis for the detention of all security internees is Geneva Convention IV. Their status is regularly reviewed and anyone no longer deemed to constitute an imminent threat to security may be released. 
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 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:
12.20. … Civilian internees must be released as soon as the reasons which necessitated internment no longer exist, but at the latest as soon as possible after the close of active hostilities.
12.21. Thus, IHL provides a code for the deprivation of liberty, for those who meet the high test for internment, and subject to procedural safeguards, for an indeterminate but not indefinite period. 
United Kingdom, Ministry of Defence, Closing Submissions to the Baha Mousa Public Inquiry on Modules 1–3, 25 June 2010, §§ 12, 12.20 and 12.21, pp. 28 and 32.
[footnote in original omitted; emphasis in original]
The UK Military Manual (1958) provides:
The exchange of prisoners of war is nowadays rare. The rule generally observed is to exchange man for man and rank for rank, with due allowance if titles of ranks or grades differ or if there is no exact equivalent. A condition is often made that the men exchanged shall not participate as soldiers in the war – in fact they are paroled. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 249.
The manual further specifies:
The exchange of prisoners may be carried out by means of so-called “cartels”. Nothing more is required than a simple statement agreed by the commanders, such agreement being arrived at by parlementaires, that is, negotiations conducted during truce, or by the exchange of letters. But for exchanges on a large scale commissioners are usually appointed, and commanders ought not as a rule in such cases to act without having previously reported to their government and taken instructions. In modern war between civilised States, an exchange of prisoners will rarely be carried out except by agreement between the governments concerned. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 250.
The UK LOAC Manual (2004) states:
8.146. [The exchange of prisoners of war during hostilities] is not a matter that is dealt with in the [the 1949 Geneva Convention III] but it is allowed by the customary law of armed conflict on such terms as may be agreed between the states concerned. The practice generally observed is to exchange soldier for soldier and rank for rank, with due allowance for differences in titles of ranks or grades. The agreement between the parties, sometimes known as a cartel, may lay down other conditions, for example, that the soldiers concerned do not take any further active role in the conflict. The agreement may be negotiated during a truce by opposing commanders, or by exchange of letters between belligerent states, often through the intermediary of a neutral state.
8.146.1. Nowadays such an exchange would rarely be carried out except by agreement at government level between the parties concerned and it is likely that the assistance of a protecting power or the ICRC would be sought. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 8.146–8.146.1.
The UK Military Manual (1958) provides:
Prisoners of war who are seriously sick are entitled to be sent back to their own country, regardless of number or rank, after having been cared for until they are fit to travel. No sick or injured prisoner of war who is eligible for repatriation under this provision may, however, be repatriated against his will during hostilities. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 251.
The UK LOAC Manual (2004) states:
A more contentious issue is whether prisoners of war must be repatriated even against their will. Recent practice of states indicates that they should not. It is United Kingdom policy that prisoners of war should not be repatriated against their will. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 8.170.
[emphasis in original]