The more I’ve thought about this the more of a bloody cheek it becomes: 
 ::U-boat commanders invariably left survivors to their fate after interrogating them about their ship (check any of these at random, if you like) so if this had happened it would only be a case of the biter bit. 
 ::And as they’d since earliest times shown no compunction at all about attacking ships that had stopped to rescue survivors, DEMS regulations were clear that no survivors would be picked up, to avoid endangering more ships; so it was official RN policy. 
 ::Despite this, U boat crews did get picked up, and Walker was no exception. He and his group  accounted for .. U-boats; where there were survivors (a lot of them were destroyed at depth, and no-one got out) he picked them up. 
 ::But it’s a shame to let the facts get in the way of a good smear…