The estimated cost of upgrading the west coast main line between London and Glasgow has more than doubled, to �5bn, Railtrack has announced.

Plans for a state-of-the-art signalling system, are being scrapped by the track and signal operator because of fears the technology will not work.

Instead the company intends to replace a tried and tested system of hundreds of signals and miles of cabling at a far greater cost.

The announcement coincides with rail regulator Tom Winsor's unveiling of a new profit regime for Railtrack. The new plans will allow the company to make a higher rate of return over the next five years from 2001, boosting profits and investment. It means Railtrack will be allowed to keep more of the revenues from the charges it levies on the train operating companies.

Pressure to improve signals

Railtrack's original vision was of a west coast line where trains ran with no signals by the tracks, controlled instead by computers in the cabs, linked by digital radio to control centres along the way.

But the company has decided it would be madness to install brand new technology overnight on a line which carries 2000 trains a day.

Railtrack has come under pressure to update its rail signals after the Paddington rail disaster in October in which 31 people died.

It had originally forecast upgrading the 450-mile line would cost around �2bn.

But the company now says that costs have risen to around �5.8bn.

It also announced a further expansion of the line, doubling capacity on certain sections from two tracks to four.

This means that the proposed upgrading of the line may not be completed until 2010.

That is likely to put the company on collision course with the rail regulator Tom Winsor, who has already warned the company it faces huge fines if it continues to delay plans for the upgrade.

Railtrack officials hinted last month they might have to ditch the computerised system, run from inside drivers' cabs, and use a different one that would take the upgrade's cost to �4bn.

On Tuesday, Railtrack director of network development Robin Gisby said: "We will meet our commitments...We will unveil a sensible signalling system."

Passengers could foot bill

The announcement comes as west coast main line operator Virgin Trains unveils its new tilting train.

There is relief that the London to Glasgow route will have known signalling technology.

Chris Green, of Virgin Trains, said: "If you want you freight railway to expand, if you want your commuter railway to expand you have to make your railways bigger.

"What Railtrack appear to be saying is that they want to invest in more track, more capacity, more flyovers."

Whether passengers will have to pay more for Railtrack's signalling decision is not yet clear.

The company hopes that the government may foot some of the bill - but the final division of costs will not be decided until the spring at the earliest.