RAF museum Hendon. A very good museum, I think it's as good as Duxford...and you won't have to travel out of London.
Look at the list of aircraft on display (including a Sunderland and Lancaster):
http://www.aviationmuseum.eu/World/E...rce_Museum.htm
I'm certain there is a Wellington too, but it's not on the list.
The Battle of Britain exhibition hall is excellent.