Motorists could be allowed to drive on the hard shoulder of the M25 under a scheme being considered by the Government.

Transport Secretary Ruth Kelly said that the emergency land could be used as an extra channel on motorways, including the M25, during busy periods after the success of a trial on the M42 near Birmingham.

Under the scheme, when traffic gets heavy, gantry signs tell drivers to slow down and spread out. The speed limit is then cut to 50mph and the extra lane is open for use.

In the West Midlands, the trial showed travel time had been cut by a quarter, despite the lower speed limit. The M6 and M40 are expected to be the first roads to get the extra lane but other roads to be considered include the M25, M4, M1 and M20.

Motoring groups have raised concerns that the hard shoulders are regularly used by the emergency services to get to crashes but the Highways Agency says the lanes would be monitored and closed if there was an accident.

The M25 west of Heathrow was last week named by the RAC Foundation as the most congested road in England.