Suspected inner ear infection, and yes he has the right oral antibiotics and steroids. This will be the second time he's been treated for it. After the first time (a couple of months back) he recovered well, but recently his head tilt has got worse and he's been more clumsy and recently seems to be a bit more subdued.
The vet had a look in his ears and wasn't able to see anything (which rules out the middle ear as the problem), and tried to take a swab but didn't have one small enough. Ear drums look fine. Basically it's either an inner ear infection or something more sinister, or perhaps just ongoing after-effects of his first infection. Another course of the oral meds (plus the drops) seemed like the best course.
Thanks for the advice on restraining him. I'll give it a go. It's quite intimidating though trying to keep him restrained when he's dealing with a sensation as strange as ear drops!