Here's a nice shot of the CO of no. 19 Squ, Brian Lane, taken at Fowlmere during the high tide of the Battle of Britain:
I guess this is the picture philip.ed was referring to when he mentioned Brian Lane wearing the prototype battledress? The fabric of the jacket seem to be different from the service dress jacket worn by the pilot on the right.
As for what was worn in the air, this picture of Bader and the rest of no. 242 Squ indicate that dress code for flying was not very strict:
