Power supply: get an OCZ stealthxstreme 2 600W. I'm extremely picky about PSU's and it's the best in the price range by a long shot. Not really all that trusting of the thermaltake psu due to various reasons i'll not burden you all with because it'll all be technical waffle.
GPU: You may as well spend the extra £10 on a gtx460 1GB now

You can get both from CCL computers for about £170 overall.
I have had a Thermaltake Toughpower 775w for over six months now and I am very satisfied by it.. High efficiency and great stable energy, and it wasn't highly priced (only $110 or so when I bought it).
Power supplies can vary hugely per product though

For example, the OCZ stealthxstreme 1 and modxstremes are complete arse
