Hi TooSoon,
I'm a little late reading this but here's to "better late than never"!! No one goes to Britain for the climate, as far as I can tell, and I've spent a fair amount of time there over the years (doing research, visiting friends, etc.). But the sun does come out occasionally, depending on where you live (mostly in the southeast!). And driving on the left-hand side of the road might be strange in the beginning, but it's surprising how quickly one can get used to it. I live in a left-hand drive place at the moment, and every time I cross the border and see cars driving on the right, I wonder why on earth they're not on the other side of the road!
For meeting people and making new friends, you could take adult ed courses, or joining local community groups ? a friend of mine is active in a nature-/bird-/bat-watching group, and another is much into a group of local astronomy buffs.
As for the art history, my background is in art history, too, and though I taught for a while, I've also used it working in museums and being a speaker for cultural tours. You might find other ways the art history comes in handy ? ways that don't appear until you're actually in the UK.
Anyway, I hope this provides a few ideas.