So he didn't go back to sleep after the 5.30am waking. I got him down for a nap at 12.15, and he went down easily. I let him sleep 2.5 hours - which I know seems like loads for a kid his age but he could have slept longer - I was a bit conflicted because I know he doesn't really make up sleep overnight but will make it up on a nap.
We changed the bedtime routine up a bit, no TV, upstairs all the way through so no 'having to go upstairs' hurdle to jump, stories in mummy's bed, then teeth, then more stories in his own bed - and touch wood he has gone down with no protest at 7.45.