A motorhome with an unladen weight not exceeding 3,050kg is subject to the same national speed restrictions as a car. A motorhome with an unladen weight over 3,050kg is restricted to 50mph on a single road and 60 mph on a dual carriageway, but is still permitted to travel at 70mph on a motorway.
The concession of car speed limits for lighter motorhomes and the limit of 70mph for heavier motorhomes on motorways does not apply to similar goods vehicles and minibuses. Hence it is important to check your V5C document has the body type correctly indicated as motor caravan.
Irrespective of the unladen weight, when you are towing a trailer with your motorhome the speed restriction is 50mph on single carriageways and 60mph on motorways and dual carriageways. Motorhomes towing a trailer may not use the right hand lane of a motorway with three or more lanes.