Hi I night-ride in cambridge with Cammtb www.cammtb.co.uk, if you come out soon you might be able to get away without lights if you don't have decent ones (you will need commuting ones at least to get back from the pub though), or post on the forum and you might be able to borrow a light.
I also ride in
Thetford (already mentioned), though I am not a big fan.
Woburn (nr Milton Keynes, about 1 - 1.5 hrs drive away)
North downs (nr Dorking, about 1.5 - 2 hrs away)
Aston Hill (Chilterns, about 1.5 hrs away)
Peaks (2.5-3 hrs away but worth it!)

There is also Chicksands (nearish woburn) and Epping forest.