Соответствующая норма
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 145. Reprisals
Section C. Proportionality of reprisals
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).