Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 6. Civilians’ Loss of Protection from Attack
According to the UK Military Manual (1958), “participation in hostilities by civilians” is an example of a punishable violation of the laws of war, or war crime, beyond the grave breaches of the Geneva Conventions. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 626(p).
The UK LOAC Pamphlet (1981) states that civilians “lose their protection [from attack] when they take part in hostilities”. 
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 3, p. 10, § 9.
The Pamphlet further states that soldiers “must not attack civilians who are not actually engaged in combat”. 
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, Annex A, p. 44, § 8.
The UK LOAC Manual (2004) states:
Civilians may not take a direct part in hostilities and, for so long as they refrain from doing so, are protected from attack. Taking a direct part in hostilities is more narrowly construed than simply making a contribution to the war effort. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 2.5.2; see also § 5.3.2 (conduct of hostilities).
The manual further states:
Whether civilians are taking a direct part in hostilities is a question of fact. Civilians manning an anti-aircraft gun or engaging in sabotage of military installations are doing so. Civilians working in military vehicle maintenance depots or munitions factories or driving military transport vehicles are not, but they are at risk from attacks on those objectives since military objectives may be attacked whether or not civilians are present. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.3.3.
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: “Civilians are protected from attack unless and for such time as they take a direct part in hostilities. Taking direct part in hostilities is more narrowly construed than simply making a contribution to the war effort.” 
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.
The manual also states: “Under the law of armed conflict, members of the civilian population lose their civilian protection when they participate in hostilities.” 
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, § 4.2.2.
At the CDDH, the United Kingdom voted in favour of Article 46 of the draft Additional Protocol I (now Article 51), describing its first three paragraphs as containing a “valuable reaffirmation of existing customary rules of international law designed to protect civilians”. 
United Kingdom, Statement at the CDDH, Official Records, Vol. VI, CDDH/SR.41, 26 May 1977, p. 164, § 119.
Upon ratification of the 1980 Convention on Certain Conventional Weapons, the United Kingdom issued a declaration stating: “Civilians shall enjoy the protection afforded by this Convention unless and for such time as they take a direct part in hostilities.” 
United Kingdom, Declaration upon ratification of the Convention on Certain Conventional Weapons, 13 February 1995, § a(iii).
In 2003, in reply to an oral question in the House of Lords asking “what in the circumstances of the Iraq of today constitutes the enemy”, the UK Parliamentary Under-Secretary of State for Defence stated: “My Lords, the potential enemy are all those, wherever and whoever they are, who seek to engage British forces in a hostile manner.” 
United Kingdom, House of Lords, Statement by the Parliamentary Under-Secretary of State for Defence, Hansard, 13 October 2003, Vol. 653, Debates, col. 600.
The UK Government Strategy on the Protection of Civilians in Armed Conflict (2010) states: “During armed conflict, civilians and combatants ‘hors de combat’ are entitled to specific protection under international humanitarian law (IHL) providing that they are not, or are no longer, taking a direct part in hostilities.” 
United Kingdom, Foreign and Commonwealth Office, Government Strategy on the Protection of Civilians in Armed Conflict, March 2010, p. 4.
(emphasis in original)
In 2010, in its closing submissions to the public inquiry into the circumstances surrounding the death of Baha Mousa and the treatment of those detained with him by UK armed forces in Iraq in 2003, the UK Ministry of Defence stated regarding common Article 3 of the 1949 Geneva Conventions: “On its face this protection is restricted to armed conflicts not of an international character. However, it is understood to apply in all forms of armed conflict as part of customary international law to set out the irreducible minimum standard.” 
United Kingdom, Ministry of Defence, Closing Submissions to the Baha Mousa Public Inquiry on Modules 1–3, 25 June 2010, § 10.2, p. 10.
The UK LOAC Manual (2004) states: “Civilians are persons who are not members of the armed forces. In cases of doubt, persons are considered to be civilians.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.3.1.
The manual specifies:
In the practical application of the principle of civilian immunity and the rule of doubt, (a) commanders and others responsible for planning, deciding upon, or executing attacks necessarily have to reach decisions on the basis of their assessment of the information from all sources which is available to them at the relevant time, (b) it is only in cases of substantial doubt after this assessment about the status of the individual in question, that the latter should be given the benefit of the doubt and treated as a civilian, and (c) the rule of doubt does not override the commander’s duty to protect the safety of troops under his command or to preserve the military situation. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.3.4.
Upon ratification of the 1977 Additional Protocol I, the United Kingdom expressed its understanding of the presumption of civilian character as only applicable
in cases of substantial doubt still remaining after the assessment [of the information from all sources which is reasonably available to military commanders at the relevant time] has been made, and not as overriding a commander’s duty to protect the safety of troops under his command or to preserve his military situation, in conformity with other provisions of [the 1977 Additional Protocol I]. 
United Kingdom, Declarations and reservations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § h.
In 2003, during a debate in the House of Commons, the UK Secretary of State for Defence, Mr Hoon, stated in reply to a question by a Member:
Alan Simpson (Nottingham, South): There have been some civilian casualties for which I am sure that even the Secretary of State would accept that there is a clear line of responsibility. They would include the seven women and children who were killed at a checkpoint and the 15 members of a single family who were killed when their lorry was attacked by an Apache helicopter. Will the Secretary of State tell the House whether current UK rules of engagement allow for such attacks on civilians; whether the rules of engagement for UK troops differ from those of US troops; whether he will place in the House of Commons Library the details of the two sets of rules of engagement; and whether he will confirm that, as has happened previously, any UK troops who were involved in instances of unjustified killings of civilians would be likely to face criminal charges?
Mr. Hoon: We do not comment in detail on rules of engagement, and certainly not on those of the United States. I would be a lot more persuaded by my hon. friend’s observations if, at the same time as mentioning the tragic deaths of seven women and children, he had also mentioned the deaths of the four US marines who were killed in a deliberate car bomb attack, perpetrated by a fanatic. In such circumstances, it is perhaps perfectly understandable – although I am not excusing it in any sense at all – that soldiers who are having to deal with a difficult situation at a checkpoint and who know that four of their comrades have been killed in that way are perhaps reacting in a way that we might not want them to. That is not to say that the accounts that have been given, again, by particular journalists are necessarily the only version of events that we should all accept. An investigation is going on into what went on at the checkpoints, and it is important that we await the outcome of that before judging the facts quite so prejudicially. 
United Kingdom, House of Commons, Statement by the Secretary of State for Defence, Hansard, 3 April 2003, Vol. 402, Debates, col. 1085.