A 500W supply with case for under £30 that's gotta be cheap and nasty. I really really really wouldn't want to use it.
I know you were trying to juggle things into the budget but like I said in my previous post anything less than stulids spec is false economy.
*edit* The only other thing I can suggest is to maybe drop the gfx card entirely from the spec and use a mobo with integrated gfx. The 4250 in my mobo and laptop can run COD4 well enough, I don't play wow so have no idea how well it would run on an integrated gpu, new games really are out the question though.
Reclaiming that £80 odd should help get everything else you need in budget then add a gfx card later. Gives you time to save some money and as time passes you may find that card is cheaper still and even better bang for buck......just a thought.