Indoors at Silverstone every week, and Taplow will be closer to you,
http://www.oople.com/forums/showthread.php?t=105640
and as you know DMS are indoors, Telstar in Milton Keynes indoors, and grass outdoors (Sat 17th see Matty above) sometimes.
Surrey & Hants are astro and floodlit so almost indoors
just need a roof etc.. (as above check they are open this Sunday)
You can get outside in Swindon and Torch - check times. (I am seeing showers Sunday, dry Saturday)