Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 1. The Principle of Distinction between Civilians and Combatants
Section A. The principle of distinction
The UK Military Manual (1958) refers to “the division of the population of a belligerent State into two classes, namely, the armed forces and the peaceful population”. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 86.
The UK LOAC Manual (2004) states:
Since military operations are to be conducted only against the enemy’s armed forces and military objectives, there must be a clear distinction between the armed forces and civilians, or between combatants and non-combatants, and between objects that might legitimately be attacked and those that are protected from attack. The principle of distinction, sometimes referred to as the principle of discrimination or identification, separates combatants from non-combatants and legitimate military targets from civilian objects. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 2.5–2.5.1.
In its chapter on air operations, the manual provides: “Parties to the conflict shall at all times distinguish between civilians or other protected persons and combatants and between civilian or exempt objects and military objectives.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 12.19; see also § 13.25 (maritime warfare).
With regard to internal armed conflict, the manual states: “A distinction is to be drawn between those who are taking a direct part in hostilities, who may be attacked, and those who are not taking a direct part in hostilities, who are protected from attack.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.6.
The UK LOAC Manual (2004), as amended in 2010, states:
Since military operations are to be conducted only against the enemy’s armed forces and military objectives, there must be a clear distinction between the armed forces and civilians, or between combatants and non-combatants, and between objects that might legitimately be attacked and those that are protected from attack. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, as amended by Amendment 3, Ministry of Defence, September 2010, § 2.5–2.5.1.
In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United Kingdom stated: “The parties to an armed conflict are required to discriminate between civilians and civilian objects on the one hand and combatants and military objectives on the other and to direct their attacks only against the latter.” 
United Kingdom, Written statement submitted to the ICJ, Nuclear Weapons case, 16 June 1995, § 3.67.
In 2003, in reply to a written question in the House of Commons, the UK Minister of State for the Armed Forces, Ministry of Defence, wrote: “Cluster bombs have been used against targets for which they were the most appropriate available weapon and where they could be used in accordance with international law, including with the principles of proportionality and discrimination.” 
United Kingdom, House of Commons, Written answer by the Minister of State for the Armed Forces, Ministry of Defence, Hansard, 8 April 2003, Vol. 403, Written Answers, col. 139W.
In 2003, in reply to a written question in the House of Commons asking whether he would “make it his policy not to use cluster bombs in urban or populated areas in Iraq”, the UK Secretary of State for Defence wrote:
Cluster bombs are only used strictly in accordance with international law. This includes the principles of distinction and proportionality as well as precautionary measures to be taken in planning and conducting an attack, as contained in the First Additional Protocol of 1977 to the Geneva Conventions of 1949. The targeting process takes account of these principles in matching the type of weapon used to the target to be attacked. There will be circumstances when it would be considered more appropriate to use other munitions than cluster bombs. These circumstances are more likely to arise in urban or populated areas as cluster bombs engage targets that cover an area. 
United Kingdom, House of Commons, Written answer by the Secretary of State for Defence, Hansard, 14 April 2003, Vol. 403, Written Answers, col. 571W.
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. In the conduct of military operations they must distinguish at all times between combatants and civilians”. 
United Kingdom, Foreign and Commonwealth Office, Government Strategy on the Protection of Civilians in Armed Conflict, March 2010, p. 4.
While the core challenges in the protection of civilians identified in the previous reports of the Secretary-General still need our sustained attention, the new report also identifies several protection policy priorities that need to be explored. In particular the following “emerging” issues would benefit from our attention, and the Group of Friends stands ready to act as a platform to advance them. …
… [O]n the issue of lethal autonomous weapons systems (LAWS), the Group is of the view that further discussions are needed and it welcomes the fact that the issue will be examined in Geneva in May 2014, in the framework of the CCW [Convention on Certain Conventional Weapons]. The Group hopes that such discussions will also examine the issue with due consideration to the protection of civilians as part of a comprehensive debate including legal, military operational, technological and ethical perspectives. In time discussion should focus on the relevance of such systems to the protection of civilians, in particular in the context of IHL and with regard to the principles of distinction, precaution and proportionality. 
United Kingdom, Statement by the permanent representative of Switzerland during a UN Security Council open debate on the protection of civilians in armed conflict made on behalf of the Group of Friends on the Protection of Civilians in Armed Conflict, namely Australia, Austria, Belgium, Brazil, Canada, France, Germany, Italy, Japan, Liechtenstein, Norway, Portugal, Switzerland, the United Kingdom and Uruguay, 12 February 2014, p. 2.