So I checked the nightcam video for the last couple of nights. He appears from under the shelf area at the opposite end of the cage to the house each night. So there I was, thinking I was being clever, putting his veg in a dish on the platform at the opposite end of the cage to the house, so he'd be encouraged to get up and walk across the cage in the evenings (this used to work with Charlie). But no, he wants to wake up very close to his veg - as he used to before!
Previously, both his food bowl and his bit of veg were on top of his house and he'd pop out of his top hole, nab the veg and pop down again.
Either he is just quite a lazy hamster and wants his veg close by when he wakes up, or I have confused him! By putting the food and veg in different places. He goes across to his house roof after he's up and had his veg, and sits there pouching his food - but otherwise it's an abandoned house! And an abandoned toilet.
So Hamster 1 Human 0

. I think I'll start putting his veg back on his house roof with his food to try and tempt him to move back into the house. Because he is in an extremely inaccessible corner, and lifting up a platform on long legs (if needed - eg to spot clean) is going to be a big disturbance and not easy.
I still haven't uploaded any nightcam videos from after he moved in, or recently - I will get round to it - it takes a bit of looking through and saving sections, before uploading them.