If you haven't already seen this detailed article on
Stalag VIIIB on Wikipedia, it's worth a look because it goes into details about the many
Arbeitskommandos (work parties) into which British and other PoWs were placed. In particular, scroll down to the subsection on British PoWs at Auschwitz, which says: "The first 200 British PoWs arrived at Auschwitz in September 1943 but over the winter of 1943 another 1,400 British PoWs (mostly captured in North Africa) were transported to [Arbeitskommando] E715". Because the factory where the E715 PoWs were employed was next to the infamous concentration camp, many PoWs witnessed the atrocities there. Escapees from Stalag VIIIB reported this to the Allies. As a consequence, in the summer of 1944 the International Red Cross visited the camp housing the E715 PoWs, (not the concentration camp) and so there will be a Red Cross report outlining conditions in the camp at that time. This will certainly be available on the ICRC website (there are currently delays in fulfilling inquiries about WW2) and possibly also at TNA (see
WO 224 in general, and particularly
WO 224/127).
There is a three volume book on the subject of British PoWs in WW2,
Prisoners of War by JB Hayward, held by TNA and the IWM among others:
https://tna.koha-ptfs.co.uk/cgi-bin/koha/opac-detail.pl?biblionumber=48771 Vol One contains details of British Army PoWs.
