Thanks.
He is actually completely better now and full of beans, so I am 100% sure that his mouth is not the issue.
This is now the 4th day he has had no breastfeed, so I am facing up to the fact that he has weaned.
I only had to express 4oz to make them comfortable on the first day of no nursing and they have been fine since, so I am working on the theory that my supply tanked. It seems rather odd that it should happen so suddenly, but he seems to have accepted it and although he still likes to snuggle into my bare boobs, does no more than have a cursory suck on the nipple before giving up!
I am sad that bf seems to be over, but it's been 15 1/2 months, so I've had a good innings and he is going down at night quite happily and sleeping well, so I guess I just have to go with it!