Ditto PORC, and the Gorrick venues. (the gorrick venues cover most of the tunnel hill, ash-vale etc venues suggested).
AFAIK, Beastway closed a coupel of years ago, ironically, when the olypic building started. . leaving. .
The other alternativeive of Brackenll forest/ swinley.
Rumor is is the 2012 xc venue, and the racing has been ongoing there for years and years. 10 mile loops are easy (as in the lap for the 100 enduro). Easy dual carriageway access from the M3, andit was MBUK venueof the year, or place to ride before you die or some-such a while back.
Good soul-riding venue or jump spot depeding on your mood. .