The government will trial road pricing technology in the next couple of years to decide whether a national scheme is viable.

Road pricing plans have come under attack from politicians and the public, with 1.8 million people signing a Downing Street e-petition last year opposing the scheme.

But the government refuses to abandon plans, according to transport minister Ruth Kelly.

"People legitimately raised concerns about privacy, fairness and how any scheme would be enforced," she told BBC Radio 4.

"What we are going to do is trial technology over the next couple of years - asking private sector companies to work with volunteers and see whether they can answer some of those fundamental issues."

The proposed technology for such a scheme is yet to be decided.

One proposed model would see GPS systems in cars integrated with road pricing computers to provide an accurate measurement of relevant charges.

Another model would work in a similar way to the congestion charge technology in London.

Last year it emerged that nearly £500m is being spent by the Highways Agency on a scheme called National Roads Telecommunications Services - an initiative to monitor traffic.

But companies involved in the programme said the technology could also be used for a road pricing model similar to the technology that supports the congestion charge in London.