Man, that's the same with me, I'm from France, and I have sometimes been to the US to buy a les paul, because it was half the price there!! So the plane ticket plus the guitar was cheaper than buying it here! I think it has to do with the dollar, that is very strong now, due to the Euro that is pretty weak (have you checked out the coins??) and to the companies who import the guitars, they have the exclusivity, so they can put the price tag they want!! add the taxes the governments have (it's 20.6% in france, I don't know in the UK)
You can see it's the same with movies, books, and video games, that sometimes go from double to triple of the price that you can have in the US or Japan...
I have bought the zen guitar CD, and with the shipping, handling, etc... I have paid it 5 dollars less than the price that I would have paid in my favorite store!! Well, it sucks...