i strongly second duxford, been there twice. their air show [twice a year iirc] is awesome, its a day trip from london..while there see the imperial war museum, & the raf museum, both can be reached on the tube w/ a little walking.

however, on your trip, if you can detour to brussels, there is a war museum which has 50 or so planes [saw a mosquito there] & a large collection of other military items...there is an old car museum about 100 yds away...both are worth the time....

i suggest you google for them in the areas you are visiting...

i'll add, just for the heck of it, comments on us museums...

i like, pensacola navy, dayton usaf, savannah mighty 8th, hartford new england air [next to the airport, go early before flight 2 hrs is about right]...
march afb, 2 in chino for a day in so cal...

enjoy.