We finally have an airdate! For the UK showing at least. Sunday January 1st, 8.10pm on BBC1.
I think I read somewhere that it's confirmed in America on PBS broadcast for May.
I've read a review (spoiler free) of the first episode which showed at the BFIs last night, and the first episode sounds utterly amazing. And yes, they do explain how they get out of the pool scene.
It's almost 1am here and I'm practically jumping around like a lunatic. I can't WAIT to see this season!