I've only seen a couple of youtube videos of Graham Norton, and he seems pretty funny. A pretty loose show.
As far as Craig on air in the UK, I don't see him going back to a network type schedule, not for a while, at least. I'd love to see him on Doctor Who

He'd be similar to early Jonathan Ross I think. Ross is far too safe and happy to plug whatever his guest wants now, Graham has always been more about the hijinks than the interview similar to Fallon.

Do you reckon he'd be better than Graham Norton or Jonathan Ross?
He was good doing his one to one interviews but he won't be able to play the Scottish card as much.
Graham Norton is good at the collective interview he does, it's like plate-spinning and Jonathan Ross is the only person the UK has ever had that resembles Leno or Letterman in his style.
Craig if in theory he would be return to Britain (that wouldn't happen) could do the same sort of shows that Adam Hills to make a name for himself.

Get him on Friday Night instead of Graham Norton. At least he's a real interviewer rather than the host of a soire between Hollywood chums which is what Norton is.