Guided busways will be installed on several sections of 150-year-old railway that ministers believe no longer carry enough people to justify their subsidy. Small guidewheels are fitted to the front of ordinary buses, which can travel at up to 60mph along the busways without the need for the driver to steer.

The buses can switch to roads at the end of the busway and take passengers to their destinations. But rail enthusiasts argue that buses are no substitute for trains and that people prefer to glide through the countryside on steel wheels running on rails rather than on tyres humming on concrete.

The Government has already approved a busway in Leigh, near Manchester, which will run on disused railway line. Alistair Darling, the Transport Secretary, is also considering a busway from Cambridge to St Ives along a 12-mile (19 km) railway line that last carried passenger trains in 1990. Another busway is planned for the disused Luton to Dunstable line in Bedfordshire.

A Department for Transport study last month proposed converting to a busway the 13-mile Severn Beach line, one of the most scenic railways in Britain, which runs from Bristol to the Severn. If the first schemes prove successful, ministers are expected to press for dozens of little-used branch lines to be converted. More than 50 branch lines covering 1,300 miles are being redesignated as 'community railways' in an attempt to cut costs by adopting lower standards of maintenance. The Government made it clear last year that it would be unwilling to continue subsidising these lines beyond 2009 unless they attracted many more passengers.

Mr Darling said: "If a line is not working, not carrying people and its costs are not coming down, then, of course, you've got to look at that."

Closing dozens of lines is deemed to be politically unacceptable, but the Government hopes to assuage rail enthusiasts by converting them to busways.

Cast Iron, the campaign to restore train services between Cambridge and St Ives, said that buses had an irredeemable image problem. Jerry Alderson, a spokesman, said: "People don't want to catch buses because, unlike trains, they are seen as cheap and demeaning. Outside London, you tend to see only women with children, pensioners and students catching buses."

He said that restoring the tracks to carry passenger trains would cost £30 million, compared with at least £86 million to construct the busway. But he acknowledged that the busway would be far cheaper to operate. The concrete guideways require little maintenance and the buses would attract more passengers with their 'door-to-door' service. Buses would run every ten minutes, compared with an hourly service on most branch lines.

Unlike bus lanes, which are frequently blocked by illegal parking, busways would be used exclusively by buses. Car traps, or pits between the concrete channels, would be dug at each end.

Bob Menzies, the head of the Cambridge busway project, said that the busway would not need any operating subsidy. "We believe that we can attract people who have two cars outside their homes but don't want to sit in congestion on the A14."

But Railfuture, which campaigns for an expanding railway, said: "This is a misguided attempt to save money which will set a dangerous precedent for rural lines. Once the bus hits the road in Cambridge it will still have to contend with all the other traffic, and delays will be inevitable. Trains have a far superior ambience."