Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 117. Accounting for Missing Persons
Section B. Provision of information on missing persons
The UK LOAC Manual (2004) states: “Each party must search for persons reported missing by an adverse party and also facilitate such searches by the provision of relevant information.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 7.38.
In 2003, in reply to an oral question in the House of Lords asking whether “the Government [would] give some priority to Kuwaiti prisoners of war and those missing in action since the previous Gulf War”, the UK Parliamentary Under-Secretary of State for Defence stated:
My Lords, I am delighted that that question has been asked, because it is one matter about which the Iraqi regime has been asked ever since the first Gulf War ended. I believe that there are 600 Kuwaiti prisoners whose whereabouts are completely unknown. Perhaps not surprisingly, the Iraqi regime has done absolutely nothing to assist the Kuwaiti authorities on that matter. We shall certainly be looking into that as matters develop. 
United Kingdom, House of Lords, Statement by the Parliamentary Under-Secretary of State for Defence, Hansard, 8 April 2003, Vol. 647, Debates, cols. 133–134.