A nationwide road-user charging scheme in which motorists might pay up to 134p a mile could be possible within 10-15 years, according to a government-established feasibility study out today.

But it would be ''a massive and complex task'' to introduce such a system that would be based on time, distance and place, and could cut congestion by a half and save £12 billion a year.

Transport Secretary Alistair Darling said ''a lot of work'' would have to be done before it was sure the scheme would work.

But he added that doing nothing about congestion was not an option and to duck the challenge on road pricing would be ''irresponsible and would condemn future generations to endless delays and increasing environmental damage''.

In the meantime, a number of congestion charging schemes - similar to that already operating in London - might be introduced.

Mr Darling said: ''I know these things are difficult and controversial. You have to take the public with you, you have to win their confidence.

''Moving to a national scheme would be fraught with difficulties. Introducing this scheme would be instead of the present (motoring tax) system. ''What we are not talking about is piling one tax on another.''