CONTROVERSIAL cameras on the M4 have slashed the number of speeding drivers on the motorway by more than half, a cabinet minister revealed in the House of Commons.

Transport Secretary Alistair Darling said the first month of the scheme had proved that the cameras are improving the safety of motorway.

But he was attacked by the Conservatives who said the cameras which are in marked vans at fixed, permanent sites between junctions 14 and 18 Hungerford to Bath are simply a cash-making operation.

Mr Darling said that the scheme by the Wiltshire Camera Partnership was successfully cracking down on speeding. "In the month or so before the speed cameras were imposed, 53 per cent of cars were seen to be exceeding the speed limit. A month later that number is down to 25 per cent.

"It does suggest that cameras do have an effect in persuading drivers to drive to the speed limit," he said.

The cameras were introduced in April. Speeding motorists now face £60 fines and three penalty points.

They have provoked fury among motorists with an estimated 400 vehicles even taking part in a go-slow demonstration.

Last month about 200 cars and motorbikes took part in a go slow demo against the cameras. Two convoys travelled at 56mph between Leigh Delamere and Membury service stations to protest against the cameras which were introduced last month.

Organiser Robin Summerhill, 52, of Chippenham, said they would keep the pressure up.

"We are quite confident that we have a high level of support," he said.

Shadow transport spokesman Greg Knight Knight urged the government hold an audit of every speed camera in the country to discover whether they are cutting speeding or simply raising cash.