At least one of these guys wasn't acting

The pilot of "F for Freddie" was played by a real bomber pilot called Charles Pickard. He was already pretty experienced by this time, having been in the RAF since 1937.

http://en.wikipedia.org/wiki/Percy_Charles_Pickard

It has been said that he didn't want the fame brought on by appearing in such a film but I can't believe anyone of his position would think it wouldn't happen. Nobody goes into that sort of thing blindly.

We'll never know the answer though; Pickard was killed in Operation Jericho - the Amiens Prison Raid - in early 1944.