By Simon Montague BBC transport correspondent

The UK Government will attempt on Thursday to allay growing concerns over the troubled modernisation of Britain's busiest rail route.

Transport Secretary Alastair Darling is expected to confirm a detailed programme of improvements for the next three years.

If this upgrading does not go ahead, it will be massively damaging and a huge setback for regional regeneration.

Louise Ellman, Labour MP

He will warn of further disruption for passengers due to engineering works, and highlight key sections of the route which are priorities for early completion.

The announcement comes after doubts this week about whether high speed trains will be forced to run more slowly on the northern part of the west coast main line.

Rising costs

Mr Darling is anxious to dispel fears that the modernisation of the main route between London and Glasgow is running into further difficulties.

The cost of the project is put at up to �10 billion, compared with Railtrack's original estimate four years ago of �2.1 billion.

The Strategic Rail Authority has denied suggestions from Railtrack that trains may have to run more slowly on the line north of Manchester, and may not be able to operate in tilting mode, in order to save money on track improvements.

The SRA has angrily insisted that it will make any such decisions, not the failed company which will shortly be replaced by Network Rail.

The SRA also said that costs are being brought under control through greater efficiency in working practices.

Past failures

The modernisation of the west coast route is seen as a classic example of disastrous project management.

It is billions over budget, way behind schedule, and a second phase intended to deliver trains running at 140mph has been shelved indefinitely.

Taxpayers will have to pick up much of the tab for Railtrack's failure to keep control. The huge cost over-runs were one of the main reasons for the government forcing the company into administration last October.

Since then, the SRA has also been forced to pay Virgin more than �100m from the public purse, to compensate for the delayed introduction of its new high-speed tilting trains.

There will be more delays during upgrades

Virgin says it will begin phasing its �1 billion fleet of 53 new Pendolino trains into passenger service from the end of this year.

The company says they will probably run between London and Manchester at first, building up to a full, tilting service between London and Glasgow by 2004.

The new rolling stock is currently being used for driver and staff training, and for test running on a 30-mile stretch of the west coast line in Cumbria.

Virgin briefly introduced the first of the trains for a once-a-day shuttle service between Birmingham and Manchester during the Commonwealth Games.

Problems with the modernisation has forced the SRA to agree to renegotiate Virgin's franchise to run the west coast route.

A new deal is due to be struck by next March and Virgin's original contract ran until 2012.

Railtrack 'playing games'

Meanwhile one member of the Commons' Transport Committee has accused Railtrack of playing games over its suggestion that trains may not be able to tilt north of Manchester.

Louise Ellman, Labour MP for Liverpool Riverside, says she learnt "with dismay that the West Coast line may not be getting the tilting trains when, as recently as last month, Virgin were telling me that the upgrading was to go ahead as planned and that there were no hitches.

Previous failures have already cost �100m

"Railtrack have already paid �100m to Virgin over their previous failures. It looks as though Railtrack, or the new Network Rail, may be involved in yet more pay-outs."

Mrs Ellman said: "Railtrack have a history of failure, and it will be unacceptable if Network Rail are to repeat the mistakes of the past.

"If this upgrading does not go ahead, it will be massively damaging and a huge setback for regional regeneration.

"This looks like a smack in the face for the entire region unless [Alastair] Darling and Railtrack can sort it out."