Sorry, I have come in a bit late on this one, my wife has been judging at Crufts.
A couple of quick points.
1.England, Scotland and Wales have exactly the same rules, but they are enacted under there different pieces of legislation.
2. It is NOT illegal to slapmark, tattoo, or eartag a weaner, but because it can (can not does) cause confusion later then (apart from any breed tattoos, which have nothing to do with legal id), it has become normal practice not to tag or otherwise weaners leaving holding of birth live to live under 12 months, and it is normal to only have a temporary paint mark. If breeder does it, then that's up to them, and if you want to then that's fine.