British war crimes are acts committed by the armed forces of the United Kingdom that have violated the laws and customs of war since the Hague Conventions of 1899 and 1907, from the Boer War to the War in Afghanistan (2001–2021). Such acts have included the summary executions of prisoners of war and unarmed shipwreck survivors, the use of excessive force during the interrogation of POWs and enemy combatants, and the use of violence against civilian non-combatants and their property.
War crimes are defined as acts which violate the laws and customs of war (established by the Hague Conventions of 1899 and 1907), or acts that are grave breaches of the Geneva Conventions and Additional Protocol I and Additional Protocol II. The Fourth Geneva Convention of 1949 extends the protection of civilians and prisoners of war during military occupation, even in the case where there is no armed resistance, for the period of one year after the end of hostilities, although the occupying power should be bound to several provisions of the convention as long as "such Power exercises the functions of government in such territory."
The Manual of the Law of Armed Conflict published by the UK Ministry of Defence uses the 1945 definition from the Nuremberg Charter, which defines a war crime as "Violations of the laws or customs of war. Such violations shall include, but not be limited to, murder, ill-treatment or deportation to slave labour or for any other purpose of civilian population of or in occupied territory, murder or ill-treatment of prisoners of war or persons on the seas, killing of hostages, plunder of public or private property, wanton destruction of cities, towns or villages, or devastation not justified by military necessity." The manual also notes that "violations of the 1949 Geneva Conventions not amounting to 'grave breaches' are also war crimes."
The 2004 Laws of Armed Combat Manual says Serious violations of the law of armed conflict, other than those listed as grave breaches in the [1949 Geneva] Conventions or [the 1977 Additional Protocol I], remain war crimes and punishable as such.