2
2657
Deleted User
Classifications that were probably defined in the age of steam driven vehicles!That is correct and the reason for the different speed limits is down to the class of vehicle (nothing to do with taxation class or type of vehicle): up to 3 imperial tons (now 3,050 kg) unladen weight is a motor car; over that is a heavy motor car.
(Over that starts to go into locomotive and others that I can't remember!)