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United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 15. The Principle of Precautions in Attack
Section A. Constant care to spare the civilian population, civilians and civilian objects
The UK LOAC Manual (2004) states: “In the conduct of military operations, constant care shall be taken to spare the civilian population, civilians and civilian objects.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.32.
In 1938, during a debate in the House of Commons, the UK Prime Minister listed among rules of international law applicable to warfare on land, at sea and from the air the rule that “reasonable care must be taken in attacking these military objectives so that by carelessness a civilian population in the neighbourhood is not bombed”. 
United Kingdom, House of Commons, Statement by the Prime Minister, Sir Neville Chamberlain, 21 June 1938, Hansard, Vol. 337, cols. 937–938.
The UK Government Strategy on the Protection of Civilians in Armed Conflict (2010) states: “IHL requires parties to a conflict to respect and protect civilians. … They must take constant care to spare civilians and civilian objects from the effects of hostilities.” 
United Kingdom, Foreign and Commonwealth Office, Government Strategy on the Protection of Civilians in Armed Conflict, March 2010, p. 4.