Radical action is necessary to cut the number of cars on Britain's roads, Alistair Darling has warned.

Speaking at a roads seminar, the transport secretary pledged to push forward plans to roll out congestion charging across the country.

And he warned motorists that new technology will also be harnessed to drive cars away from Britain's "under severe pressure" roads.

Darling warned that Britain faced a stark choice over the coming decades; more motorways or a radical rethink.

"It seems to me that in order to deal with the pressures over the next 20-30 years, we ought to look at the opportunities that are now being presented to us with new technology in order to deal with the pressures that we face," he said.

"And pricing for roads is just one of those matters that I think we need to look at."

Earlier in the week he pledged that the government would not make money from the idea - which could be as much as 10 years away - and highlighted the success of the London congestion scheme.

The transport secretary also revealed that he wants to develop a pay-as-you drive system based on satellite tracking devices fitted inside cars.

Darling says his department is willing to risk the wrath of parents by discussing ways to cut traffic chaos caused by the "school run" with education secretary Charles Clarke and his officials.

Options include changing school start times and school bus services.

"If you take this morning, at 8.50am, one in five cars on the road will be on the school run. There are other things you can do to help there. We're already looking at the American-style yellow buses," he told the BBC.

"Charles Clarke and I are looking at perhaps staggering the opening of schools so that their hours are rather different."

His big idea will, when technology allows it, use global satellite positioning as a base for a system of toll charging.

Under such a system rush hour travel would be priced the highest in a bid to cut the school run and reduce the level of commuting by car.

The system would benefit people who use their cars only on an occasional basis and cut the tax burden for many drivers, Darling claimed.

Liberal Democrat transport spokesman Don Foster welcomed the new sense of radicalism following Darling's remarks.

"At last some imaginative thinking from Alistair Darling. With congestion rising and costing British businesses over £20 billion a year he should have acted sooner," he said.

"Britain urgently needs measures that target the most congested areas of the country without penalising those in rural regions who often have no choice but to use their cars.

"The public needs a safe, affordable and reliable alternative to their car if Britain's roads are ever going to see a reduction in traffic and congestion."

Environmental groups also welcomed Darling's more radical tone, and urged ministers to push reforms on to the statute book.

Friends of the Earth's transport campaigner, Roger Higman, said: "At long last the government appears to accept that road-pricing is needed to tackle the volume of traffic on our roads.

"But it isn't the only answer. There should be far greater investment in affordable, safe and reliable alternatives to the car to cut congestion and help tackle climate change."

The group claims that the number of cars on the road has risen by seven per cent, despite government attempts to get people out of their cars.

It also suggests that public transport costs have increased whilst the cost of running a car has fallen.