FLEETS face the prospect of compulsory tracking devices in each of their vehicles as the Government considers billing motorists for road use.

A similar plan is already on the drawing board for foreign lorries visiting Britain, to be implemented in 2006, but Transport Secretary Alistair Darling has revealed the same scheme could also be applied to cars.

He said the move would be an effective way of easing congestion, charging a premium for drivers to use busy routes at peak times, while routes might be free of charge at quiet times.

'We are some way down the road to looking at the technology. We have plans to monitor lorries, but what is new is the idea of monitoring 24 million cars.

'If you accept that principle with lorries, it seems difficult to see why you shouldn't have a discussion about cars,' Darling said in an interview with the Sunday Times.

'Every motorist has got to accept there has to be some constraint. Road pricing is likely to be a better long-term solution.'

The Government has repeatedly insisted that it has no plans to introduce road tolls on A-roads and motorways, leaving congestion charging in urban areas to local authorities.

Earlier this month Transport Minister David Jamieson said: 'There are no plans to introduce inter-urban road user charging.'

But anticipating Darling's new train of thought, he added: 'We shall want to see what lessons can be learned from practical experience with charging schemes, including the national scheme for lorries announced in the recent Budget.'

Earlier this year a report from the Commission for Integrated Transport, called Paying for Road Use, argued that direct charging for road use could raise £5.7 billion a year and reduce congestion by 44%.

In one case study, it claimed a salesman covering 30,000 miles a year would incur £1,800 a year in congestion charges, but this would be offset by a £600 reduction in fuel tax, while the driver would save five days a year, worth £2,000, thanks to lower congestion.