Andrew May gurgled happily, sounding much like
they were saying:

JOOI & OT what happens to a vehicle number when the vehicle is scrapped.
Does it return to the pool of numbers for sale to people as a
personalised plate or is it lost forever?

Lost forever.

It can be transferred off for up to six months after the MOT expires, but
only by the registered keeper, and they may well ask to inspect the donor
vehicle to make sure there's no ringing going on.