PC Gaming on a budget - UK

Hello all!

I am in the market for a PC that I can use for gaming but am on a fairly tight budget. My current set up is the family pc (Intel Quad Core, GeForce GT220, 3GB ram) and it's starting to struggle. Games like GTA IV have a few frame rate issues but are playable, but Alan Wake had a frame rate of less than 10FPS, making it unplayable. My aim is for a PC that will play the next few year's releases at a playable frame rate. I'm not worried about max settings but just to be a little 'futureproof'*.

Any suggestions of sites to buy components (I am proficient in PC construction) or somebody selling their old rig? I am in the UK so sites like Newegg are a non starter.

Thanks for taking the time to read!

Rich

*as much as I despise the term.