Neil,
I've had a quick look, and,
Depends what you're after - open or disused airfields. I can't think of any sites with detailed airfield maps (i was looking for a couple myself last week)
For open airfields I can suggest the following book, which has charts for most UK airfields
UK Airports and Airfields: A Spotter's Guide (Tim Laming)
The following link has a catalogue of most UK airfields ever in existance, and links to the corresponding aerial photos and OS maps on multimap.com
http://www.homepages.mcb.net/bones/06airfields/Finally, for very general labelled layout sketches try
http://www.thunder-and-lightnings.co.uk/spotting/I think you'll be hard pressed to find decent quality charts due to copyright etc, but I might be wrong...
Cheers
Charlie