I'd be inclined to fit a 13amp unswitched FCU behind the oven - just in case some engineer came to mend the oven, and said it's out of guarantee because no 13amp fuse.
However, tomorrow I'd be probably inclined to say something completely different, and say that the 16 or 20 amp mcb or rcbo is perfectly adequate, and that if the oven goes wrong, and it's more involved than a simple element, I'd probably say I won't bother with an engineer, and I'll get a whole new oven, partly because it's filthy dirty, and I don't want to clean it anyway.