Swinley, any of the MoD lands like Tunnel Hikl (though not easy to find the trails) and then there’s Surrey Hills which is a huge area and has the best stuff really. The latter, if you head for Peaslake and ask around or just follow people you’ll find a fair bit. There’s more over in Leith hill, and even over on the north downs, though harder to find the good stuff.
Swinley is marked trails and well groomed, if a but cobbly on the hard pack, and there’s not much elevation.
There’s loads of xc all about and little spots on the many common lands surrounding Woking.
There’s even a signposted MTB trail going out of the town, although I’ve yet to find what it is, other than a walking trail, unless they mean that. It’s about 10 minutes of non fun. Still, nice to see the council making an effort. There’s a lot of cycle route signs about the town and along the canal. There’s also the Wey canal which runs down to Guildford or all the way up to the Thames.