Paul,
As Martin is in Crete right now, I thought I'd butt in and point you towards the following publisher:
http://www.ianallansuperstore.com/cgi-bin/index.cgi
At Martin's suggestion I recently bought and received two Squadron histories by Chris Ward. According to Martin he wrote many Squadron histories that still are to be equalled. I couldn't find anything on 50 Sqn, for example, and got all I need in this book. Also got the unit history of 78 Sqn in.
7 Sqn is available too. click on the military icon (the tank, NOT the aviation one!!) then enter SQUADRON PROFILES in the Search field and Bob's your uncle.
Ward used the PRO and many other books and sources for his research.
That would have been my second tip; The PRO, but I am sure you already thought of that.
I myself have been trying to find info on 7 sqn for my own research, but came up with nothing so far.