Peter: the UK in December cannot be as bad as Anchorage in mid-February. (yes, I did that once to visit friends! Cold. Largest Icicles I have EVER seen. Saw moose, eagles, otter and a caribou race that was hysterical.) It can be worth going in the off season sometimes, but I'll heed your warning about London. Sydney would be a better choice perhaps
Checked out the website for X2. Very cool. Looked like it was based on a set. I would like that as a set at least.