AIR 27 for the operational record books themselves (on microfilm mainly)
AIR 16 for Fighter Command files (things such as tactics and battle orders)
AIR 15 for Coastal Command files
AIR 14 for Bomber Command
Also, the RAF Museum archive section (you need to make an appointment to visit) and the Air Historical Branch (ditto re: appointment) may have useful material depending upon how much depth you want to research to. Anything you're after in particular?
Yes,just realised im a mong,as i was looking in wrong part of national archives. Im after the squadron diarys for battle of britain time, just got some stuff about it and wanted to do further research.