M.Joshi writes:

Surely from the basic formula, P = I * V the required fuse for the oven
would be around 15A or am I missing something here?

* All these things (appliances, cookers, fuses, breakers) have a fair
tolerance. The mains voltage can be a few percent out too. Though
fuses and breakers will carry their rated load continuously and
probably a bit more.

* There may not be a regulation saying you can't but what if the
cooker's manual did say that it must be on its own circuit, the
cooker were to burst into flames one day and burn your house down
(because of a fault rather than the way you wired it) and the
insurance company found out.

Jon