Motoring organisations are calling for an increase in the national speed limit on Britain’s motorways. Campaigners say the limit should be raised to 80mph — the speed at which many drivers routinely travel. Unless the limit is increased, they say, there is a danger that tens of thousands more drivers will be caught by speed cameras being newly installed on motorways to enforce the 70mph limit. The resulting increased number of prosecutions could lead to protests and to otherwise law-abiding motorists being unfairly penalised. The RAC Foundation will this week begin preparing a campaign to raise the motorway limit to 80mph.

Speed cameras have appeared on the M4 in Wiltshire — the first time they have been used outside roadworks to enforce motorway limits. Two mobile camera sites have been set up between junctions 11 and 13 of the M74 in Strathclyde and will be in place by the summer.

The clampdown on motorway speeds has provoked widespread unease. “A limit of 80mph in good weather at a safe distance from the car in front is a safe speed,” said Edmund King, executive director of the RAC Foundation.

“Modern cars have better brakes and safety systems and can be driven safely at higher speeds — 80mph has been the common-law limit for almost a decade now. Until recently, at least, you were highly unlikely to be pulled over for doing anything up to 85mph.”

The RAC wants the government to raise the motorway limit and at the same time introduce a motorway driving exam as a supplementary test for all new drivers. The Department for Transport (DfT) said it would consider the RAC’s arguments. “We looked at the idea of raising the speed limit but it was ruled out on road safety grounds,” said a spokesman. “The government will now certainly consider the RAC Foundation proposal, and of course any decision will depend on who is in government in a few days’ time.”

The AA Motoring Trust, the campaigning arm of the Automobile Association, said it may add its voice to the campaign if the use of speed cameras spreads. “Many motorists who believe the limit is too low do not want it raised for fear of disturbing current enforcement custom and practice,” said

Andrew Howard, the head of road safety for the AA Motoring Trust. “But if camera enforcement on motorways were to become widespread, it may be necessary to raise the speed limit.”

The Association of British Drivers (ABD) said the 70mph limit was outdated. “In 1965 when the 70mph limit was first introduced, 70mph represented more than 80% of the maximum speed of average cars,” a spokesman said. “Now it represents only 60%.”

A protest group backed by the ABD has been formed to campaign against speed cameras on motorways. “M4 Protest” is planning a slow drive along the M4 through Wiltshire next Saturday. “I hope drivers will turn out in big numbers,” said the campaign founder Robin Summerhill, 52, a housing consultant who says he is frustrated by speed cameras in his area of Wiltshire. “The motoring public is at breaking point and these cameras are the last straw.”

A recent study of 1,000 drivers by the Transport Research Institute at Napier University, Edinburgh, and the Transport Research Laboratory in Crowthorne, Berkshire, found that the number of motorists driving at “excessive” speeds (more than 90mph) on the motorways had increased.

Asked what was the fastest speed at which they would drive on the motorway and still feel safe, all interviewees gave speeds ranging from 80-100mph.

Enforcement of the 70mph limit on the motorway network is varied. Police have tended to turn a blind eye to drivers who break the limit by a margin of 10mph or less, and usually book only motorists exceeding 85mph. A transport department report found that more than half of all cars on motorways already exceed the speed limit and a fifth travel at more than 80mph. Of those interviewed for the survey, 51% were in favour of an 80mph limit. Of that group, 27% wanted the new limit to be strictly enforced, while 24% said existing enforcement levels would be adequate.

Speed cameras have been used on motorways only in special circumstances: to enforce temporary reduced speed limits at roadworks; at dangerous junctions; and, as on the southwest section of the M25, during periods of congestion.