Hmmm, well the mart usually create the movement documentation; the buyer tells them the destination address and holding number, haulier details, etc, and they print off the docs for you.
if he's going literally directly from the mart to the slaughterhouse he'll need to give the mart the full address and holding number of the slaughterhouse and the vehicle reg, haulier details etc of whoever is taking them (in a proper livestock trailer or wagon.) The mart would give him the documentation, he would get the haulier section signed by the haulier then hand the documents to the slaughterhouse who should sign for receiving the animals, return the haulier's copy to the haulier and send off the top copy to their local trading standards office. If he would be taking them to a stopover in lairage outwith the slaughterhouse then he'd give the mart the details of the lairage - which would need a holding number - and then when he takes them to the slaughterhouse do a complete AML (animal movement license) for the journey from lairage to slaughterhouse.
HTH
Sally