Right, back from vets.
He was fussing a bit when they were trying to get blood from him, vet reckons he had some sort of localised skin reaction to the clippers (no I've no idea either) so they put some anaesthetic cream on to numb the area so he didn't jump when they put the needle in.
Blood tests, urinalysis, and a newish treatment for arthritis (Solensia) which the vet suggested might sort out his incontinence as "if it's painful to walk, it's just easier for him to piss where he is rather than go to the litter tray". If that works it's a monthly injection and it ain't cheap but oh well, I don't want him in pain and this is safer for his kidneys than other treatments.
About his kidneys, it's not great news hence the tests, one is enlarged and we need to find out whether it's an infection or now final stage CKD as the treatment/management will differ.
He seems happy enough which is the main thing and while he seems happy I'm not going to make any rash decisions - he'll let me know when it's time and we don't seem to be quite there yet even though he's a bit frail and doddery. The test results may tell us otherwise of course, but we'll deal with that once we have more information.