Silver Tabby British Shorthair
You can see the rather faint but distinct classic "M" mark on the forehead that tells us that he is a tabby cat. Not that we need that to tell!
He appears to be a mackerel tabby but it is not clear from the photo. In fact on second thoughts it seems to be a classic or blotched tabby pattern.
Nice cat and nice photo. You can see the nice cobby, solid body conformation of this cat breed in this photo.