Соответствующая норма
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 128. Release and Return of Persons Deprived of Their Liberty
Section D. Voluntary nature of return
The UK Military Manual (1958) provides:
Prisoners of war who are seriously sick are entitled to be sent back to their own country, regardless of number or rank, after having been cared for until they are fit to travel. No sick or injured prisoner of war who is eligible for repatriation under this provision may, however, be repatriated against his will during hostilities. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 251.
The UK LOAC Manual (2004) states:
A more contentious issue is whether prisoners of war must be repatriated even against their will. Recent practice of states indicates that they should not. It is United Kingdom policy that prisoners of war should not be repatriated against their will. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 8.170.
[emphasis in original]