Getting across town is becoming slower and more frustrating

Researchers found that the success of London's congestion charge has made an expanded, national plan seem viable.

In future, instead of buying a paper tax disc, road users will probably have to pay as and when they travel.

The study said the new system would be needed as more motorists switched to greener fuels to escape tax.

Tax levels

Both the government and research companies are examining how Britain should develop its road network in the face of growing car and commuter numbers.

The Economic and Social Research Council recently commissioned a report on the future of motoring taxation and what part it was likely to play in the future.

The research team, headed by Dr Stephen Potter, found that one of the main problems facing the government is how to keep tax revenues steady, while at the same time offering incentives for consumers to switch to less polluting fuels.

Will congestion charging spread out across the UK?

It found that the government is set to lose about �2bn a year from cuts to tax on low emission fuels, with that figure rising as newer technologies, such as hydrogen- and electricity-driven vehicles, come on the market.

As a result, it reckons the government will have no choice but to scrap road and fuel tax and replace it with a "pay-by-the-mile" system.

"Because car ownership is such a central feature of our lives it is viewed as political suicide for any government to raise vehicle or fuel taxation to a level that will produce significant behavioural change," the report said.

Computer checks

Under the proposed scheme, drivers would have onboard equipment to register where and when they drove, probably having to pay more if they went out at rush hour or ventured into congested areas.

While it would be at least a decade before that became a reality in the UK, a similar system may be up and working in the US within five years, the report said.

The effects of traffic congestion are highlighted in a separate report from the Chartered Management Institute.

It found that 79% of managers surveyed had missed important business meetings because of travel delays.

Two out of every five, meanwhile, said that travel problems increased their irritability at work, while almost half complained it had caused them to miss a family commitment, such as reading a bedtime story to a child.

The CMI said that changing the way we work may be the best way to combat the problems associated with increasing car numbers and congestion.