Found this :
The Geneva Convention makes provision for the repatriation of all Prisoners of War, even during hostilities. During 1939-1945 it was only possible for the British and Germans to reach agreement over the seriously ill and disabled. For the majority of the 40,000 British servicemen who were taken prisoner in 1939 and 1940, the war was to be a very long and dispiriting experience.
Negotiations, conducted through the Red Cross, over the repatriation of seriously wounded men, had begun in late 1940. They did not progress very far because there were far fewer German men in this category than British. It was only after substantial numbers of Germans were taken prisoner in the Desert campaign of 1942 that the talks resumed. The actual exchange of prisoners did not take place until October 1943:
https://ww2today.com/19th-october-19...and%20disabled.
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