Hello Dave,
As far as I can make out, most of the WW2 German POW records, which were held by the British, were sent to Germany in the 1950's.
WASt. The German Archive,
[www.com-de.pair.com] maybe able to help, but they do tend to take a long time answering, anything up to six months is not unusual.
The only thing of any major interest I have found concerning U-Boat survivors at TNA/PRO is here.
[www.ubootwaffe.net]
If you do find any new leads or information, please post on this forum.

regards
Roger