A leading Welsh motoring expert has predicted road pricing will become a reality after the government announced plans for "pay-as-you go" road charges.
The government says the charges are needed to cut congestion
But Professor Garel Rhys, of Cardiff University's Centre for Automotive Industry Research, said it should not be an excuse to cut road building.
Plans to charge drivers by the mile to cut congestion, were revealed by transport secretary Alistair Darling.
The proposals would replace road and fuel tax.
The transport secretary told newspapers the change was essential if Britain was to avoid "LA-style gridlock".
According to the reports, every vehicle would have a black box to allow a satellite system to track its journey, with road pricing starting from as little as 2p per mile in rural areas.
Professor Rhys said: "I think eventually there will have to be a major system of road pricing in the UK.
Drivers could soon be charged for every mile they drive
"The key is trying to introduce those tolls without affecting the flow of traffic, that is, not having to stop and pay at a booth which caused congestion itself.
"Also you have to be careful with the precise pricing, you don't want to divert traffic off the major highways onto "rat runs" which are free.
"These proposals will start a great deal of debate.
"I think the government will have to show this is not just simply a system of charging for the existing road network, soaking the people who are using it, but also use it as a price signal where it will show where new roads are really needed."
The professor said that the government would have to convince road-users that the charges would be beneficial.
"This should not be an excuse for a zero road building system," he said.
"Many of the instances of congestion are due to road works or accidents not to the total amount of traffic.
"Sixty percent is congestion and 40% is due to the interruption of traffic flow for various other reasons.
"We have the longest shutting of roads for accident clear ups of any country in the developed world."
He said that policing the scheme could become a problem.
"The vast majority will be law-abiding but what about the minority? There could be a sizeable one.
"People want to go from A to B and they will resent any attempt to price them out of the market.
"It shouldn't be an additional tax, something should happen to other things. Say, the petrol tax or excise duty should effectively come down to zero.
"Governments will upset at their peril society's wish to do what it wants to do and that is to move around."