Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 152. Command Responsibility for Orders to Commit War Crimes
The UK Military Manual (1958) states that the responsibility of military commanders for war crimes “arises directly when the acts in question have been committed in pursuance of an order of the commander concerned”. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 631.
The UK LOAC Pamphlet (1981) provides: “If a soldier carries out an illegal order, both he and the person giving that order are responsible.” 
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 10, p. 38, § 1.
The UK LOAC Manual (2004) states:
16.35. Individuals are responsible for the war crimes that they commit themselves or which they order or assist others to commit.
16.35.1. Article 7 of the Statute of the International Criminal Tribunal for the former Yugoslavia provides that “a person who planned, instigated, ordered, committed or otherwise aided and abetted in the planning, preparation or execution of a crime … shall be individually responsible for the crime.”
16.35.2. The Rome Statute of the International Criminal Court also confirms that an individual is responsible for a war crime if he:
a. commits the crime himself, on his own or jointly with others, or
b. orders, solicits or induces a crime which is committed or attempted. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 16.35–16.35.2.
In 1991, a spokesperson of the UK Foreign and Commonwealth Office stated that the Minister of State, Foreign and Commonwealth Office, had summoned the Iraqi ambassador and had reminded him “of the personal liability of those who authorised [the] use [of chemical or biological weapons] and asked that Iraq would not use them”. 
United Kingdom, Statement by a spokesperson of the Foreign and Commonwealth Office, 21 January 1991, reprinted in BYIL, Vol. 62, 1991, p. 680.
In 1993, in a “Non-Paper” discussing the 1993 ICTY Statute transmitted to the UN Legal Counsel, the UK Foreign and Commonwealth Office stated: “Under the Geneva Conventions those who order the commission of a grave breach are as responsible for it as the actual perpetrators.” 
United Kingdom, Foreign and Commonwealth Office, Non-Paper, Former Yugoslavia: War Crimes Implementation of Resolution 808, 22 March 1993, reprinted in BYIL, Vol. 64, 1993, p. 700.