weekdays most airforce/ army/ navy bases. Weekends though are usually no fly days. Middle wallop good for student pilots lynx and various other choppers. Yeovilton is good for the navy choppers and harriers plus a good museum, wallop also has a museum. Boscombe down, while a pain to find places to spot, has a huge variety of planes to see. RAF valley in wales has alot of hawks.

I dont know to much about what goes on at fairford. I would imagine you can see alot of american aircraft when they are in town

A good place to see military aircraft is the various low-level practice areas around the country. I found a site with fantastic photos taken at these locations & tips for the best spots. Unfortunately I've lost the link. I'll look around for it.

I've been to one of these spots myself, at Mold in North Wales, but that was many years ago. http://www.bbc.co.uk/wales/northeast/panoramics/pages/moel_famau.shtml

PS. I think the best places for watching these aircraft would be the various events & air displays held all over the country. There's usually at least one such event every weekend throughout the season. You can see a variety of different types at most air shows & providing you can persuade 'er indoors it makes a good day out for the whole family. This would mean waiting a while as the display season doesn't start untiil May. Here's a list of the more important ones for this year so far. http://www.aeroflight.co.uk/shows/showdate.htm

thats part of the reason its a pain to spot there. I have heard of a few people getting pictures there. Its just best not to hang around the perimeter. but hey you work there so your more up to date than i am with their rules:)