Drivers who ignore smart motorway lane closures face a £100 fine and three penalty points of their licence from March.

Highways England believes ignoring red X signs on overhead gantries is "dangerous" and expects penalties to be introduced next spring.

It has issued around 80,000 warning letters to drivers who have broken smart motorway rules since December 2016, with around a third relating to driving in closed lanes.

Road-side cameras which automatically detect lane violations are "currently being tested by the Home Office", the government-owned company wrote in a document seen by the Press Association.

"We would expect enforcement of red X offences to commence from spring 2018," it added.

Incidents could be treated like passing through a red traffic light, which carries a fixed penalty of £100 and three penalty points.

Smart motorways involve using the hard shoulder for traffic unless a red X indicates it is closed, normally because of an accident or broken down vehicle.

Sections of the M1, M4, M5, M6 and M42 have already been modified, with 480 lane miles being added to England's motorway network.