Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice relating to Rule 66. Non-Hostile Contacts between the Parties to the Conflict
The UK Military Manual (1958) states:
386. It is on occasions unavoidable – and often convenient – for commanders to open direct communication with the enemy for military purposes. Furthermore, humanity and convenience may at times induce them for special reasons to relax the general prohibition of intercourse between belligerents. …
387. It is essential that in such non-hostile relations the most scrupulous good faith should be observed by both parties, and that no advantage be taken which is not intended to be given by the enemy. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, §§ 386 and 387.
The manual also provides:
There is nothing in [Articles 32–34 of the 1907 Hague Regulations] which indicates that a white flag is the only method whereby one belligerent may signify to the other its desire to open communications. In modern conditions of warfare wireless messages and loud-speakers are also used as a means of conveying the wish of one belligerent to communicate with the other. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 394, footnote 2.
The manual further emphasizes:
420. A suspension of arms is essentially a military convention of very short duration, concluded between commanders of armies, or detachments in order to arrange some local matter of urgency: most frequently to bury the dead, or to collect and succour the wounded, or, occasionally, to exchange prisoners, to permit conferences.
497. A cartel, in the wider sense of the term, is issued to signify a convention concluded between belligerents for the purpose of permitting certain kinds of non-hostile intercourse which would otherwise be prevented by the conditions of war. For instance, communication by post, trade in certain commodities, and the like, may be agreed upon by a cartel. In its strictly military sense, however, a cartel means an agreement for the exchange of prisoners of war. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, §§ 420 and 497.
The UK LOAC Pamphlet (1981) states:
It is within the legal competence of an officer to arrange for a temporary cease-fire for a specific and limited purpose, for example to permit the collection or evacuation of the wounded … Absolute good faith is required in all such dealings [the arrangement of a cease-fire] with the enemy. 
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 4, p. 17, § 18.
The UK LOAC Manual (2004) states:
Principle of Good Faith
10.2. Whenever there are non-hostile relations between parties to an armed conflict, those relations must be conducted with the utmost good faith and any agreement reached scrupulously observed. In particular, there should be no abuse of a flag of truce or emblems of identification in dealings between belligerents. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 10.2.
In its chapter on negotiations between belligerents, the manual further states:
Humanitarian arrangements to be specifically agreed may include … the provision of medical care or food supplies … An armistice agreement cannot take away the protection afforded to individuals under the law of armed conflict, though it can improve upon that protection. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 10.24.
On the basis of a meeting with an army lawyer, the Report on UK Practice comments that negotiation with the enemy “is a tricky area now” owing to the practicalities of fast-paced modern warfare. 
Report on UK Practice, 1997, Meeting with an army lawyer, 18 July 1997, Chapter 2.2.
The UK Military Manual (1958) states:
From time immemorial a white flag has been used as a signal by an armed force which wishes to open communications with the enemy. This is the only meaning which the flag possesses in international law. The hoisting of a white flag, therefore, means in itself nothing else than one party is asked whether it will receive a communication from the other. It may indicate merely that the party which hoists it wishes to make an arrangement for the suspension of arms for some purpose; but it may also mean that the party wishes to negotiate for surrender. Everything depends on the circumstances and conditions of the particular case. For instance, in practice, the white flag has come to indicate surrender if hoisted by individual soldiers or a small party in the course of an action. Great vigilance is always necessary, for the question in every case is whether the hoisting of the white flag was authorised by the commander. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 394.
The UK LOAC Pamphlet (1981) states: “The white flag, or flag of truce, indicates no more than an intention to enter into negotiations with the enemy. It does not necessarily mean a wish to surrender.” 
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 4, p. 16, § 10.
The UK LOAC Manual (2004) states:
10.5. From time immemorial, a white flag has been used as a signal of a desire to open communications with the enemy. This is the only meaning that the white flag possesses in the law of armed conflict. Wilful abuse of a white flag that results in death or serious injury is a grave breach of Additional Protocol I.
10.5.1. The display of a white flag means only that one party is asked whether it will receive a communication from the other. In some cases it may also mean that the party that displays it wishes to make an arrangement for a temporary suspension of hostilities for a purpose, such as the evacuation of the wounded, but in other cases it may mean that the party wishes to negotiate for surrender. Everything depends on the circumstances and conditions of the particular case. For instance, in practice, the white flag has come to indicate surrender if displayed by individual soldiers or a small party in the course of an action.
10.5.2. Those who display a white flag should cease firing until the invitation has been answered. Any abuse of a white flag is likely to be a war crime. Great vigilance must, however, always be displayed in dealing with enemy forces that have displayed a white flag, because other enemy soldiers in the vicinity may be unaware of the display of the white flag and continue firing. This is especially likely where the decision to display a white flag was taken not by the enemy commander on behalf of the entire force under his command but by individual soldiers. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 10.5–10.5.2.
A training video produced by the UK Ministry of Defence emphasizes that the white flag is protective and that it only indicates a wish to negotiate, not to surrender. 
United Kingdom, Ministry of Defence, Training Video: The Geneva Conventions, 1986, Report on UK Practice, 1997, Chapter 2.2.
The UK Military Manual (1958) states: “The usual agents in the non-hostile intercourse of belligerent armies are known as parlementaires.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 389.
The manual also states:
A person to be regarded as a parlementaire must be authorised by one of the belligerents to enter into communication with the other and must present himself under cover of a white flag. The authorisation [for a parlementaire to enter into negotiations] should be in writing and be signed by the sending commander. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 393.
The UK LOAC Manual (2004) states:
Negotiations between belligerent commanders are normally conducted, at least in the first instance, by an intermediary, known technically as a “parlementaire”, normally operating under a flag of truce, who has been authorized in writing under the signature of the sending commander. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 10.4.
The UK Military Manual (1958) states:
The commander to whom a parlementaire is sent is not obliged to receive him in every case. There may be a movement in progress the success of which depends on secrecy, or owing to the state of the defences, it may be considered undesirable to allow an envoy to approach a besieged locality. In direct contrast, however, to a former rule, it is now no longer permissible – except in cases of reprisals for abuses of the flag of truce – for a belligerent to declare beforehand, even for a stated period, that he will not receive parlementaires. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 398.
The UK LOAC Pamphlet (1981) provides: “There is no obligation to receive a flag party which may be sent back.” 
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 4, p. 16, § 10.
The UK LOAC Manual (2004) states:
The commander to whom a parlementaire is sent is not obliged to receive him in every case. However, it is no longer permissible for a belligerent to declare beforehand, even for a stated period, that he will not receive parlementaires. However, the commander is entitled to take all steps necessary to protect the safety of his position or unit and to prevent the parlementaire from taking advantage of his visit to secure information. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 10.8.