What Car? Q and A - Who's allowed in the third lane

Q: I have seen an increasing number of vehicles using the outside lane of a motorway recently, what are the rules regarding this?
David Butterworth

A: There are three types of vehicles that should not use the outside or right-hand lane of a motorway. These are: any vehicle drawing a trailer; a goods vehicle which has a maximum weight when fully loaded of 7.5 tonnes; or a passenger vehicle which has been constructed or adapted to carry more than eight passengers, in addition to the driver, which weighs more than 7.5 tonnes.

There are exceptions to this, such as in an emergency, or when instructed to do so by a police officer.