I'd recommend the i5-3570K, but it might be 10-15 pounds outside your price range. A good motherboard to go with that would be the Gigabyte GA-Z77X-UD3H. Both the processor and the the motherboard are well suited to overclocking.
Match that with either a B75 or H77 motherboard and you have a pretty potent and fairly cheap solution. There's a lot of motherboard options depending on what features you might want in the future, and whether or not you want a full sized ATX board or are happy enough with a mATX board (these days you don't loose much at all). If you are value-hunting, the ASRock H77M or B75M are both very well priced.
The i5 3570K is great, but once you factor in the more expensive motherboard you need, and a solid aftermarket CPU cooler, the added value evaporates a little.
For £50, you can't complain too much at that graphics card. A new card to offer you similar performance is likely to set you back at least £150. Even if it lasts you a year or so, it's a pretty good buy.