Welcome mate - I dont think you can go wrong with either Scott scale 70 or a marin palisade. For the money they are both good bikes. They both have good geo. Id say the scott is more XC and the palisade more trail, but they are pretty similar.
Both well established brands. Most important thing is to buy it from a good bike shop -
http://www.tritoncycles.co.uk/ is also worth checking out.
Also get a test ride if you can - its worth a million hours spent reading reviews in the intraweb
any of these would do the trick as well - quite like the paint job on that trek
http://www.tritoncycles.co.uk/products. ... 1b0s2p6617http://www.tritoncycles.co.uk/products. ... 1b0s2p4408http://www.tritoncycles.co.uk/products. ... 1b0s2p5637the quality of bikes you can get for £800 these days is amazing.