Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 46. Orders or Threats That No Quarter Will Be Given
The UK Military Manual (1958) states: “It is forbidden to declare that no quarter will be given.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 117.
The UK LOAC Pamphlet (1981) provides: “It is forbidden … to declare that no quarter will be 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. 12, § 2(c).
The UK LOAC Manual (2004) states: “It is prohibited to order that there shall be no survivors, to threaten an adversary therewith or to conduct hostilities on this basis.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.5; see also §§ 12.23 (air operations) and 13.29 (maritime warfare).
With regard to internal armed conflict, the manual states: “It is prohibited to conduct military operations on the basis of a denial of quarter.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.11.
In its chapter on enforcement of the law of armed conflict, the manual notes:
The Hague Regulations 1907 are now recognized as part of customary law. Those regulations provide that the following acts are “especially forbidden”:
d. to declare that no quarter will be given. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.27.
Under the UK ICC Act (2001), it is a punishable offence to commit a war crime as defined in Article 8(2)(b)(xxi) and (e)(x) of the 1998 ICC Statute. 
United Kingdom, ICC Act, 2001, Sections 50(1) and 51(1) (England and Wales) and Section 58(1) (Northern Ireland).
In the Eck case (The Peleus Trial) before the UK Military Court at Hamburg in 1945, the commander of a German submarine was charged with ordering the killing of survivors of a sunken Greek merchant vessel. He was found guilty and the Judge Advocate ruled that it must have been obvious to the most rudimentary intelligence that it was not a lawful command. 
United Kingdom, Military Court at Hamburg, Eck case (The Peleus Trial), 20 October 1945.
In the Von Falkenhorst case before the UK Military Court at Brunswick in 1946, the accused, Commander-in-Chief of the German armed forces in Norway, was found guilty of having incited, in two orders of October 1942 and June 1943, members of the forces under his command not to accept quarter or to give quarter to Allied soldiers, sailors and airmen taking part in commando operations. Furthermore he had ordered that, in the event of the capture of any Allied soldiers, sailors or airmen taking part in such operations, they should be killed after capture. 
United Kingdom, Military Court at Brunswick, Von Falkenhorst case, Judgment, 2 August 1946.
In the Wickman case before the UK Military Court at Hamburg in 1946, the accused was found guilty of “committing a war crime … in that he … in violation of the laws and usages of war gave orders to [his] platoon that no prisoners were to be taken and that any prisoners taken were to be shot”. 
United Kingdom, Military Court at Hamburg, Wickman case, Judgment, 26 November 1946.
In the Von Ruchteschell case before the UK Military Court at Hamburg in 1947, the accused was charged, inter alia, of having ordered that survivors on life-rafts be fired at. He was found not guilty of this charge. 
United Kingdom, Military Court at Hamburg, Von Ruchteschell case, Judgment, 21 May 1947.
In the Le Paradis case before the UK Court at Hamburg-Altona in 1949, a German officer was convicted of the killing by his troops, on his orders, of members of a UK regiment which had surrendered. 
United Kingdom, Court No. 5 of the Curiohaus, Hamburg-Altona, Le Paradis case, 25 October 1948; see also cases cited in Lassa Oppenheim, International Law. A Treatise, Vol. II, Disputes, War and Neutrality, Longmans, Green and Co., London/New York/Toronto, Seventh edition, Hersch Lauterpacht (ed.), 1952, §§ 69 and 109; Eric David, Principes de droit des conflits armés, Bruylant, Brussels, Second edition, 1999, § 2.167; Christopher Greenwood, The Customary Law Status of the 1977 Geneva Protocols, in Astrid J. M. Delissen and Gerard J. Tanja (eds.), Humanitarian Law of Armed Conflict: Challenges Ahead. Essays in Honour of Frits Kalshoven, Martinus Nijhoff, Dordrecht, 1991, p. 106.
In 1995, during a debate in the House of Lords in 1995, the UK Minister of State, Home Office, criticized the Geneva Conventions (Amendment) Bill introduced by a private member for categorizing as grave breaches certain acts not treated as such in the 1977 Additional Protocol I, including threatening an adversary that there shall be no survivors. 
United Kingdom, House of Lords, Statement by the Minister of State, Home Office, Hansard, 25 May 1995, Vol. 564, cols. 1083–1084.