Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 105. Respect for Family Life
Section B. Reunion of dispersed families
The UK Military Manual (1958) states:
Belligerents must facilitate enquiries by members of families dispersed as a result of the war, with the object of renewing contact between them. They must also facilitate the work of approved organizations engaged in this task. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 38.
The UK LOAC Manual (2004) states:
The belligerents, and all parties to Additional Protocol I, are required to facilitate in every possible way the reunion of families dispersed as a result of armed conflict, to deal with their enquiries and (subject to security regulations) to facilitate the work of approved organizations engaged in this task. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 9.11.