I'm going to take you at your word and limit myself to PC World only. You might well get a better deal elsewhere, but if you're happy with them, that's fine.
Depends on your budget really. Looking on their website, for desktop, go either i5-2xxx or better still i7-2xxx (they are under Core i5 and Core i7 respectively). Budget from £400-£1200. The i7 machines will only really differ in memory - this is something you can probably upgrade cheaper yourself if you feel confident... Personally, I'd go i7-2600 + 8GByte memory with Win7 64bit, but you can definitely get away with 4GB if you want to (although it MAY mean changing 2 x 2GByte memory sticks for 2 x 4GByte memory sticks should you want to upgrade).
As to laptop, I'd stick with second gen i5/i7 again (you know they are second gen as they have the i5-2xxx or i7-2xxx processor). Again, lots to choose from there, but the problem with laptops is they tend to only have 1366 x 768 screens which isn't much if you're displaying 10+Mpixels on them. Again, choice down to price and features you want.
