I don't know whether you have it over there but we have a product called metatone tonic. It's basically a blend of vitamins and minerals meant as a pick me up for people who have lost their appetite after illness or whatever but it works well for dogs and such too. My sister told me about it because it is well known among guinea pig breeders to use this if a piggy goes off their food. She uses it on her piggies and it always gets them eating again.
I've used it on my dogs if they are a bit off colour, say if the weather is really hot and they are turning their nose up at too many meals to feel comfortable. It always gets them eating again.

I take it he has been ill but I haven't read anything so I'm a but clueless here.

It's a good idea to go back to the vets if he doesn't start eating again by tomorrow. It's good that he's still drinking though, at least he's still getting fluids.

If you can find anything like metatone tonic, it's worth trying it. There isn't anything in it that would hurt a dog and it just provides them with some nutrients whilst they aren't eating and helps them feel better.