I've just spotted the earlier post with link (broken) to "croft community trails".
That's what we're working on, but there's still loads to do to get it up to scratch.

We do night rides most Fridays. Join our facebook group (Croft Trails) or mbswindon.co.uk for updates
Locally you've got:
-ridgeway (Swindon - Malborough)

wider:
Mendips
Cwm Carn (near Newport, Wales) cross country loop (hard) and a downhill track. The downhill can be ridden on a cross country bike.

Afan Argoed (near Port Talbot)
Forest of Dean loads of tracks, single track, downhill and the FODCA trail.

Wales also has Brechfa, Nan y Arian, Penmachno, Coed-y-Brenin, Betw-y-s-coed, Llandegla
All purpose built cross country trails.

There's loads of trails being built around the place, plus miles of bridleways.

Red Planet bikes in Swindon do Tuesday night rides.