Règle correspondante
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 145. Reprisals
Section E. Termination of reprisals as soon as the adversary complies again with the law
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).