I had taken the 15 inch MBP into consideration, but only for a short amount of time. While I do like bigger screens with desktops, I prefer smaller ones with laptops, I just think it would be to bulky and heavy for me, so I wanted to stick with 13 inch models. Also, I am not from the US nor from the UK, so eBay is only an option if they ship worldwide, but then it has to be dirt cheap because it adds up with shipping. Where I'm from, the older 15' MBPs are like 100-150 Euros more expensive than 13 inch ones, so that's an issue as well. Another thing is, based just by benchmarks, the iMacs just seem a whole lot faster than any MBP, so that's my concern as well.
Understand that. My beef with the 13's is the screen resolution - I actually prefer the physical size, but 1200x800 is just not enough (the 15" is 1440x900, and that little bit does make a pretty big difference). Have you checked Amazon? They have a UK page, so I assume they'd have resellers much like the US page. As for the price difference, I completely understand - that's the reason I'm still rockin' an 09 mini and a crappy Dell laptop - holding out for a new MBP in the future!