Leatherhead is 10mins from Boxhill, and about 15mins from Westcott which is at the bottom of Leith Hill. Both of these have excellent riding and the bike shop in Westcott called Nivarna Cycles does evening rides. If you check out their website it will have the details.
As for accomodation I know their is a Youth Hostel actually on Holmbury Hill (next to Leith Hill) which is right in the centre of lost of riding and this is about 20 mins from Leatherhead