Feeling a bit more hopeful now I've spoken to Jo, as we've got a plan
She's had a look through all the tests done so far, and isn't worried about the blood results. The anaemia and muscle wastage is to be expected in a bun that's moving about. Unfortunately the xrays aren't good enough quality for her to see the lesion, and as they were conscious ones (I had asked for full xrays under GA) his joints aren't in the right place to really see what's going on.
So he's booked in for Tuesday to have an examination, then full xrays under heavy sedation and whatever else we need to do to get to the bottom of this.
He's got another vet puzzled, but we'll get there in the end!
Thank you. Yes, she'll do skull xrays and recheck teeth too.