Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 145. Reprisals
The UK Military Manual (1958) states: “Reprisals between belligerents are acts of retaliation for illegitimate acts of warfare. One of their objects is to cause the enemy to comply in future with the recognised laws of war. Reprisals are by custom admissible as a means of securing legitimate warfare.” It further states: “The illegitimate acts in respect of which reprisals are admissible may be committed by a government, by its military commanders, or by some person or persons whom it is impossible, for the time being, to apprehend, try and punish.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, §§ 642 and 643.
The manual also notes:
Reprisals are an extreme measure of coercion, because in most cases they inflict suffering upon innocent individuals. Nevertheless, in the circumstances of war, they often provide the only remedy as a punishment, as a deterrent and as a means of inducing the enemy to desist from his unlawful conduct. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 644.
In addition, in a footnote on a provision regarding the procedure before recourse to reprisals is made, the manual states: “A certain caution should be exercised before deciding to institute reprisals, as in some cases counter-reprisals may follow, thus defeating the purpose of the original reprisals.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 646, footnote 2.
The UK LOAC Pamphlet (1981) states: “Under customary law reprisals are permitted to counter unlawful acts of warfare. They can only be taken if: a. they are intended to secure legitimate warfare.” It also states: “Reprisals are an unsatisfactory way of enforcing the law. They tend to be used as an excuse for illegal methods of warfare with a danger of escalation through repeated reprisals and counter-reprisals.” However, the manual also states:
The United Kingdom reserves the right to take proportionate reprisals against an enemy’s civilian population or civilian objects where the enemy has attacked our own civilians or civilian objects in violation of [the 1977 Additional Protocol I]. 
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, §§ 14, 15 and 17.
The UK LOAC Manual (2004) states:
Enforcement of the law of armed conflict can involve a wide variety of measures. “Enforcement” is taken here to mean action to ensure observance of the law and also action that may be taken following alleged or actual violations. Action aimed at effective enforcement of the law can include, but is not limited to:
k. Reprisals by an aggrieved state. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.1.
The manual further states:
16.16. Reprisals are extreme measures to enforce compliance with the law of armed conflict by the adverse party. They can involve acts which would normally be illegal, resorted to after the adverse party has itself carried out illegal acts and refused to desist when called upon to do so. They are not retaliatory acts or simple acts of vengeance. Reprisals are, however, an extreme measure of coercion, because in most cases they inflict suffering upon innocent individuals. Nevertheless, in the circumstances of armed conflict, reprisals, or the threat of reprisals, may sometimes provide the only practical means of inducing the adverse party to desist from its unlawful conduct.
Conditions for reprisal action
16.17. In order to qualify as a legitimate reprisal, an act must comply with the following conditions when employed:
a. It must be in response to serious and manifestly unlawful acts, committed by an adverse government, its military commanders or combatants for whom the adversary is responsible;
b. It must be for the purpose of compelling the adversary to observe the law of armed conflict. Reprisals serve as an ultimate legal sanction or law enforcement mechanism. Thus, if one party to an armed conflict breaches the law but then expresses regret, declares that it will not be repeated and takes measures to punish those immediately responsible, then any action taken by another party in response to the original unlawful act cannot be justified as a reprisal;
e. A reprisal must be directed against the personnel or property of an adversary;
g. It must be publicized. Since reprisals are undertaken to induce an adversary’s compliance with the laws of armed conflict, any action taken as a reprisal must be announced as such and publicized so that the adversary is aware of the reason for the otherwise unlawful act and of its own obligation to abide by the law. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 16.16–16.17.
The manual also restates the interpretative declaration made by the UK upon ratification of the 1977 Additional Protocol I (see infra). 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.1.
During discussions on reprisals in Committee I of the CDDH, the United Kingdom stated that it was “not true that at the present time [in 1976] the old system of lawful counter-measures was excluded; it still existed under customary law, and any exclusion must be expressed, as in the Geneva Conventions”. It also stated that it would “support the principle embodied in [the French proposal on a prohibition of reprisals]”. 
United Kingdom, Statement at the CDDH, Official Records, Vol. IX, CDDH/I/SR.47, 29 April 1976, p. 74, § 38.
In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United Kingdom stated:
A belligerent reprisal is an action, taken by a party to an armed conflict, which would normally constitute a violation of the laws of armed conflict but which is lawful because it is taken in response to a prior violation of that law by an adversary … To be lawful, a belligerent reprisal must meet two conditions … It must meet the criteria for the regulation of reprisals, namely that it is taken in response to a prior wrong … [and] is undertaken for the purpose of putting an end to the enemy’s unlawful conduct and for preventing further illegalities. 
United Kingdom, Written statement submitted to the ICJ, Nuclear Weapons case, 16 June 1995, p. 58.
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 this would be true “to the extent that it considers such measures necessary for the sole purpose of compelling the adverse party to cease committing violations under those Articles”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § (m).
The UK Military Manual (1958) states:
An infraction of the laws of war having been definitely established, every effort should first be made to detect and punish the actual offenders. Only if this is impossible may recourse be had to reprisals, if the injured belligerent is of the opinion that the facts warrant them. As a rule, the injured party must not at once resort to reprisals, but must first lodge a complaint with the enemy (or with a neutral Power, for transmission to the enemy) with a view to preventing any repetition of the offence and to securing the punishment of the guilty. This course should always be pursued unless the safety of the troops requires immediate drastic action and the persons who actually committed the offences cannot be secured. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 646.
The UK LOAC Pamphlet (1981) states that reprisals can only be taken if “prior warning is given”. 
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, § 14(b).
The UK LOAC Manual (2004) states:
16.17. In order to qualify as a legitimate reprisal, an act must comply with the following conditions when employed:
b. It must be for the purpose of compelling the adversary to observe the law of armed conflict. Reprisals serve as an ultimate legal sanction or law enforcement mechanism. Thus, if one party to an armed conflict breaches the law but then expresses regret, declares that it will not be repeated and takes measures to punish those immediately responsible, then any action taken by another party in response to the original unlawful act cannot be justified as a reprisal;
c. Reasonable notice must be given that reprisals will be taken. What degree of notice is required will depend upon the particular circumstances of the case;
d. The victim of a violation must first exhaust other reasonable means of securing compliance before reprisals can be justified. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.17.
The manual also restates the interpretative declaration made by the UK upon ratification of the 1977 Additional Protocol I (see infra). 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.1.
In a 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 … It must meet the criteria for the regulation of reprisals, namely that it is … a means of last resort.” 
United Kingdom, Written statement submitted to the ICJ, Nuclear Weapons case, 16 June 1995, p. 58.
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 this would be true “only after [a] formal warning to the adverse party requiring cessation of the violations has been disregarded”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § (m).
The UK Military Manual (1958) states:
What kinds of acts should be resorted to as reprisals is a matter for consideration by the injured party. Acts done by way of reprisals must not, however, be excessive. They must bear a reasonable relation to the degree of violation committed by the enemy. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 648.
In a footnote relating to this provision, the manual refers to the Nuremberg trials and states:
Acts of reprisal that are grossly excessive against non-protected persons … constitute a war crime. During the Second World War German forces applied a “hundred to one” order in occupied territories, whereby one hundred civilians would be seized at random and shot as a reprisal for the killing of one German. On occasions civilians already held as prisoners were shot in the same proportion. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 648, footnote 1.
The UK LOAC Pamphlet (1981) states that reprisals can only be taken if “they are in proportion to the violation complained of”. 
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, § 14(c).
The UK LOAC Manual (2004) states:
A reprisal must be in proportion to the original violation. Whilst a reprisal need not conform in kind to the act complained of, it may not significantly exceed the adverse party’s violation either in degree or effect. Effective but disproportionate acts cannot be justified as reprisals on the basis that only an excessive response will forestall further violations. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.17.
The manual also restates the interpretative declaration made by the UK upon ratification of the 1977 Additional Protocol I (see infra). 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.1.
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 … It must meet the criteria for the regulation of reprisals, namely that it is … proportionate … It has been argued that the use of nuclear weapons could never satisfy the requirements of proportionality … This argument, however, suffers from the same flaws as the argument that the use of nuclear weapons could never satisfy the requirements of self-defence. Whether the use of nuclear weapons would meet the requirements of proportionality cannot be answered in the abstract: it would depend upon the nature and circumstances of the wrong which prompted the taking of reprisal action. 
United Kingdom, Written statement submitted to the ICJ, Nuclear Weapons case, 16 June 1995, pp. 58–60.
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 be disproportionate to the violations giving rise thereto”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § (m).
The UK Military Manual (1958) states: “Although there is no clear rule of international law on the matter, reprisals should be resorted to only by order of a commander and never on the responsibility of an individual soldier.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 645.
The UK LOAC Pamphlet (1981) states that reprisals can only be taken if “they are ordered at a high level”. For cases in which the United Kingdom should have recourse to reprisals against the enemy’s civilian population or civilian objects, the manual states that “the decision to do so will be taken at Government level”. 
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, §§ 14(e) and 17.
The UK LOAC Manual (2004) states: “As reprisals entail state responsibility, they must only be authorized at the highest level of government.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.17; see also § 5.18.
The manual also restates the interpretative declaration made by the UK upon ratification of the 1977 Additional Protocol I (see infra). 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.1.
The manual explains:
This means that reprisals taken in accordance with the statement are permissible by and against the United Kingdom. However, commanders and commanders-in-chief are not to take reprisal action on their own initiative. Requests for authority to take reprisal action must be submitted to the Ministry of Defence and require clearance at Cabinet level. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.2.
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 such measures would be taken “only after a decision taken at the highest level of government”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § (m).
The UK Military Manual (1958) states: “If the enemy ceases to commit the acts complained of, reprisals must not be resorted to; if reprisals have already begun, they must at once cease.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 649.
The UK LOAC Pamphlet (1981) states that reprisals can only be taken if “they cease when the violation complained of ceases”. 
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, § 14(d).
The UK LOAC Manual (2004) states: “Reprisal action may not be taken or continued after the enemy has ceased to commit the conduct complained of.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.17.
The manual also restates the interpretative declaration made by the UK upon ratification of the 1977 Additional Protocol I (see infra). 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.1.
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 “such measures [will not] be continued after the violations have ceased”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § (m).