I think some of our questions could be answered by getting high res scans of certain bits of the photo, such as the book (probably a ledger book if it's from the stores), the medal ribbons, cap badges etc.
For now, I've been looking at the chap front and centre, and whilst I am in no way an expert in these things, is he wearing a ribbon for the Air Force Cross? It has diagonal red and white stripes. Have attached small clip from the photo, to illustrate (hopefully!)
Prue