Luna's suggestion has worked! I annoying ended up with the camera so it couldn't see his wheel well enough on Friday night, but I re-positioned it last night and have some long videos of him happily running.
However, I discovered at 4am this morning when I thought I heard a noise that he was chewing the bars behind the wheel. I suspect that it's because he wants to do more free roaming. He has a tendency to get up no more than half an hour before I go to bed (and I'm currently doing sleep CBT so I have to go to bed at a set time). This morning he was up at 8.30am, which is late for him, and when I spoke to him he wanted to come out and play! I don't think he's got the brains to work out he needs to get up earlier, so I will try and convince him to get up and play a couple of hours before I go to bed.
Ria - I love the way you have Rory's cage set up and I think Merry would like that too. I just don't want to touch his wheel now it's working
But I will use it for inspiration to improve his cage to hopefully help with the bar biting.
flowerfairy - I like the Trixie wooden wheel - cheaper and quieter than the Silent Runner. But my last hamster wee'd on it and the current one has been weeing on his wheel too, and plastic is just a lot easier to deal with.