I give you the Leighton/Linslade Century. 100 miles of Beds, Bucks and Herts finest trails. The route takes in the awesome Sustrans route 6 AND 51. If you can survive that then next you'll have to face the wildest trails that the banks of the Grand Union Canal can offer the mountainbiker, and these do get narrow in places. Get through that and you'll be rewarded with a chance to recover on some quiet country lanes, but don't let your guard down quiet they may be, but in some places there are NO road markings.
September 6th put it in your diary and bung it in your man bag.