I might not need to go for the live fish. I put a smelt in his viv this afternoon and had a feel of Vimes before I left him alone, his body tone is getting bad - he just feels empty and floppy. So I told the wife that the next time I visit an aquatics shop I'll be buying half a dozen guppies (I'll need to buy half a dozen as buying a single shoaling fish would raise questions).

I went into the office a couple of hours later and the fish wasn't in the dish. I can't see it laying around the viv, and Mr Vimes is coiled up with just his head and a few loops visible so I can't see whether he's got a fish in him and I don't want to dig around and disturb him.
I've just checked my records, he last ate on the 15 October - that makes almost exactly 10 months since his last meal (12 weeks of that he was in brumation). In that time he's dropped from 46g to 40g.

I'm now hoping that this is a turnaround. I'll have a good look in the viv tomorrow and add a couple more smelt to the dish. But I'm more optimistic now than I have been with Vimes.