Knowing how badly overpriced PCworld is i have only once ventured in with the intention of buying anything and this was because my psu exploded, badly needed a new one and it was good friday so Computer Orbit(my usual) was closed that day.
What i was after was any PSU 300W or greater, i had looked up the prices on the day and in my local shops i could have bought a 450W for under 15 pounds. On finding the supplies in PC world i found thier cheapest at about 25 pounds was a piddly 230W supply, that kind of difference is just inexusable. Needless to say i just waited. Too many people use PC World because it is all they know, anybody who asks me about buying a new computer or hardware(frequently , its what i do for a living) is warned foremost NOT to buy here! Even after my charges for call out and installation the pc world price of just the part is still more!
Bottom line, ask somebody who knows where is a good place to buy in your area, or if you're comfortable with it, online.
gael