don't know if you will find a 4770 for that amount in England - with a 400watt PSU you may have to go with a 4670, which is still a pretty good little card if you are gaming at lower resolutions (1440x900 or less in most newer games would be ok).
I am just going to give you a link to Tom's Hardware. They do a monthly "Best card for the Money" review for each price range. http://www.tomshardware.com/reviews/...card,2404.html
Much better than giving an opinion.