Camp 357 was a Stalag and also called Kopernikus.

http://www.rafcommands.com/Air%20Force%20PoWs/RAF%20POWs%20Camp.html

The number is his recorded PoW number in the 1944/45 updated lists from the Red Cross

http://www.rafcommands.com/Air%20Force%20PoWs/RAF%20POWs%20Query%20S_1.html

It is possible that he filled in a PoW Liberation report on this release and return into the UK. This will be held at The National Archives Kew.

Also at Kew is the AIR 27 Operations Record Book for the unit which will give the known details of this last and previous flights with the squadron. This is available for download in month bites at the approximate price of a pint (even on Bank Holidays)

Regards
Ross