The M4 is often choked with holiday traffic

The finding comes in a survey of 15,000 vehicles for the National Motorway Month Group, which includes the RAC Foundation and the Highways Agency.

The group warns that getting too close contributes to a third of motorway accidents where someone is injured.

It is calling for more chevrons on the motorways to help keep vehicles at least two seconds apart.

The Association of Chief Police Officers has already indicated it is backing a new generation of traffic cameras that can detect tailgating.

It wants a change in the law to make it a specific offence so that on-the-spot fines can be issued.

The survey found as many as 70% of drivers were guilty of tailgating on some stretches of motorway.

Don't tailgate, don't drive when tired, don't hog the middle lane and take extra care through roadworks Transport Minister David Jamieson

The highest risk area was found to be on the M4 near Maidenhead, Berkshire.

On average over the whole motorway network, 41% of drivers were too close to the vehicle in front, the report suggested.

It said that tailgating decreased in chevroned areas, and remained lower than average for some miles afterwards.

Transport Minister David Jamieson said: "Motorway safety is a responsibility for all of us. We are constantly striving to design and deliver safer motorways, but motorists need to take care, follow the road rules and also use common sense.

'Frightening'

"Don't tailgate, don't drive when tired, don't hog the middle lane and take extra care through roadworks - that way the roads are safer for all road users."

Edmund King, executive director of the RAC Foundation, said: "It is frightening that more than 40% of motorists are driving too closely on our busy motorways, especially as tailgating can lead to serious accidents and road rage.

"Tailgating limits the ability of motorists to be able to react swiftly to events which may be happening further along the motorway, and significantly increases the chances of a motorway pile-up.

"We would urge drivers to obey the rule of keeping two seconds back from the vehicle in front and adjust their distance according to local weather conditions."