Règle correspondante
United Kingdom of Great Britain and Northern Ireland
Practice relating to Rule 66. Non-Hostile Contacts between the Parties to the Conflict
Section D. Refusal to receive parlementaires
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.