Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 58. Improper Use of the White Flag of Truce
The UK Military Manual (1958) provides: “Improper use of a flag of truce or of signals of surrender is forbidden. The flag must not be used merely to gain time to effect a retreat or bring up reinforcements.” 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 318.
In connection with the requirements for granting the status of combatant, the manual notes in particular that irregular troops should be warned against improper conduct with flags of truce. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 95.
The manual further states: “In addition to the ‘grave breaches’ of the 1949 [Geneva] Conventions, … the following are examples of punishable violations of the laws of war, or war crimes: … abuse of … a flag of truce”. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 626(d).
The UK LOAC Pamphlet (1981) provides: “It is forbidden … to make improper use in combat of a flag of truce.” 
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. 12, § 2d.
The UK LOAC Manual (2004) states: “It is prohibited to … misuse deliberately in an armed conflict other internationally recognized protective emblems, signs or signals, including the flag of truce.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.10.
In its chapter on negotiations between belligerents, the manual states:
It is forbidden to make improper use of a flag of truce. Thus, a feigned intention to negotiate or surrender with the intention of using the white flag as cover for the collection of information might amount to the war crime of perfidy whatever the consequences. It would amount to a grave breach of Additional Protocol I if it resulted in death or serious injury. A parlementaire who abuses his position in this way can be taken as a prisoner of war and tried. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 10.10.1.
With regard to internal armed conflict, the manual provides: “It is prohibited to make improper use of the flag of truce.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.13.
In its chapter on enforcement of the law of armed conflict, the manual states:
The Hague Regulations 1907 are now recognized as part of customary law. Those regulations provide that the following acts are “especially forbidden”:
f. to make improper use of a flag of truce. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.27.
Under the UK ICC Act (2001), it is a punishable offence to commit a war crime as defined in Article 8(2)(b)(vii) of the 1998 ICC Statute. 
United Kingdom, ICC Act, 2001, Sections 50(1) and 51(1) (England and Wales) and Section 58(1) (Northern Ireland).
A training video on IHL produced by the UK Ministry of Defence illustrates the rule that the false use of emblems is forbidden. 
United Kingdom, Ministry of Defence, Training Video: The Geneva Conventions, 1986, Report on UK Practice, 1997, Chapter 2.4.