you need a CPH number before you can buy a micro pig, piggy clicky
Also check the deeds to the property that you live in, or intend to the keep pig at if different, that there are no Covenants prohibitting the keeping of pigs there.
Ah! I used to work in the department that dealt with Animal Health which was governed by DEFRA. I was getting confused with the slap mark with pigs, but you need a holding number. Piglets can't have a slapmark as they are too young.