Cat's breath?

I see by your post your British! My Granddad 7 generations back came from Sus!! Back your your 'moggy'.....here in the US we call them mixed breeds; it sounds as if your cat has some dental/gum problems. Cats mouths are hard to keep clean( they really don't like brushing!) so they get a build up of cat food and hair sometimes in their cheeks and around their teeth. I would pop into your local veterinary office to let them look at your cat's teeth and gums. The vet may need to have your cats teeth cleaned and that would set him/her right again! Cheerio!