I will probably bump the HDD up to a cavier black or even a Velociraptor
I will also add another GPU in the future for SLI
I can add another £100 to my build maybe but i would like to see a build within my price limit so all suggestions are very welcome
Forgetting about Sandy Bridge and forgetting that the LGA1156 platform is "dead" and offers no upgrade path down the road.....
Overall that is a good build. My suggestions are below.
HDD / SSD - Replace the WD with a Samsung Spinpoint F3. ...or... Use your additional money and buy an SSD for a boot drive (OCZ Agility 2 or similar with a SandForce controller), then buy a 1TB or 2TB drive for additional storage.
GPU - The GTS 450 is a good card, but consider an HD 5770. If you have a good idea you are going with multiple GPUs later, then stick with the GTS 450 or opt up for a GTX 460.
PSU - Again... If you have a good idea you are going with multiple GPUs later, step up the PSU past 600w. Antec, OCZ or Corsair... Maybe this one => http://www.ebuyer.com/product/235519
Yeah, nice build in general, but since we're so close to the new platform, might as well check out the official reviews and benchmarks before making a decision one way or the other.
One thing I'll say though, that you're better off with a P55 board for a (presumably) gaming build.
Also, I don't see an ODD in your build. Do you plan to re-cycle one from your old PC? If so, you can do that with your HDD as well for now. Maybe add an SSD in a year's time when the prices come down a bit. Just make sure you have your connectors in place if your current system is a bit long in the tooth and has IDE drives.