I'm not going to dig through the site, but here's what you should be looking for...
CPU: X3 440
Mobo: Gigabyte GA-770TA-UD3
RAM: Any non-OCZ 2x2 GB 1333 mhz CL 9
GPU: HD 5770 (it'd help if we knew your monitor's resolution)
HDD: Seagate 7200.12 500 GB or Samung Spinpoint F3 500 GB
Case: Antec 200 or 300 or Coolermaster 690
PSU: Any 400-500W unit from Corsair, Antec, SeaSonic or Silverstone. OCZ will do as well, just make sure to get at least a 500W unit.
Optical: The cheapest SATA DVD burner you can find
In the US, that totals about $580, which is just about 400 pounds...
At least it means that some people don't have to go to the effort of digging up an online currency converter.
Anyway, seeing as some of the parts I suggested here aren't available anymore, I would suggest checking other sites to see if you can get all of those parts without amendment and cheaper. Overclock.co.uk is probably the best one to check out atm. Or changing the build to look like this:
i can repost this in New System Build if you want, sorry for bad placing, Thank you for helping
Silvune i mesured my case and it isnt big enough so i need a new case too but because im no good at finding componenets that will fit into the motherboard and such i thought because everyones so helpful here that they could help.
I think Silvune's setup is a good one the only changes I would make is getting a 4870 graphics card from aria (£93.99 but no free postage so allow £100) this should give similar or better performance than the 5770 though without the 5 series features and save £36 you need another £10 for 4Gb Ram which you can get by either an Athon x2 250 processor or a cheaper motherboard (on this budget any AM3 should be fine). As for the case I think on this budget you could go for a lesser brand PSU ie Sumvision PowerX2 700W PSU - 2x SATA 1x PCI-Express £19.99 leaving £25 for a case of your choice. I think you are best with the 4Gb RAM and the 4 series card what does everyone else think?
I DO think the 4 series card is a prudent way to shave cost without giving up performance ... The 5 series features are not likely to be missed (especially with OP's titles) and driver updates should address any multimedia requirements.
You Brits scare me with the PSUs you will "try" ... Here in the USA, we are fearful of anything "less" than Corsair/Seasonic/Antec ... You must have better emergency response services.
500~550Watts ... MORE than enough headroom.
Cases? ... You are on your own ... READ REVIEWS (worst-first).
Or you could change to an Athlon II X2 250 if you need the 1GB frame buffer, which apparently is important for higher resolutions or enabling AA.
One of the reasons I suggest sticking with a 5770 is because they use less power than a 4870, so it would put less strain on the PSU. Here's the review I read of the PSU I'm recommending http://www.hardwarelabs.de/be_quiet!_Pure_Power_L7_350W_&_530W-Fazit_3166 As you can see (if you can read german or get google or some other site to translate it) it is a positive review. It shows good voltage regulation, high efficiency and quietness. Seeing as the review isn't as indepth as say a review on jonnyguru would be then I think taking a precaution like using less power hungry components is a good idea. Also it's called a 530W PSU because Be Quiet actually think the 12V rail can deliver 530 watts, which I think is an encouraging sign.