NETWORK Rail has been given the go-ahead by the Office of Rail Regulation to complete work on the £8.6 billion West Coast main line modernisation by December this year.

The decision has been welcomed by Network Rail but has gone against the wishes of Virgin Trains and freight company EWS which had called for the project completion to be extended until May 2009.

The passenger and freight companies fear the major disruption will drive customers away if the work is pushed through before Christmas this year, because of the number of engineering closures that will be needed.

Virgin also wants more time to train drivers for the extra services.

The ORR had ordered Network Rail to produce a plan showing how it could complete the work by December to enable new timetable improvements to be made.

The move followed the disastrous engineering overruns in the New Year at Rugby, Liverpool Street and in Scotland.

But the industry regulator warned Network Rail about mitigating the effect of disruption caused by engineering work, and said that it would be closely monitoring delivery of the plan.

Michael Lee, ORR director of access planning and performance, said: "The West Coast main line is a key part of the national rail network, linking London, Birmingham, Manchester, Liverpool and Glasgow.

"Network Rail's planned improvements will mean better services for passengers across a wide part of the network from December this year.

"We have scrutinised this plan, making use of expert independent advice, and considering the views of those who run services, representatives of those who use them, and the government bodies that provide funding.

"It is clear that most people want to see the improvements made this year.

Passengers will unfortunately face increased disruption while this work is being done, but will benefit from the new timetables in December 2008. We are very conscious of the adverse impact on rail freight, and Network Rail needs to do all it can to ease the effect of its engineering work on users of the railway.

"It is vital that Network Rail now delivers this plan."

Following the New Year engineering work, the ORR began an investigation into the overruns at Rugby and Liverpool Street. As a result, Network Rail was fined £14 million and a "provisional order" was placed on the company to deliver a robust plan to the ORR by the end of March 2008 for the completion of the West Coast project.

Welcoming the decision Iain Coucher, Network Rail's chief executive, said: "This news puts us on firm ground to press ahead with our plans to complete the £8.6bn project to transform services on the West Coast main line.

"Our plans deliver a big prize for passengers and freight users alike in the shortest time possible with 30 per cent more long-distance services and significantly improved journey times across the West Coast route by the end of the year.

"We recognise that this massive engineering undertaking will continue to cause disruption to services along the route for the rest of the year, especially at weekends and bank holidays but the significant benefits that will be delivered make it more than worthwhile.

"Continued close working with all train operators on this, and neighbouring routes will help to keep passengers and freight moving and disruption to a minimum."

Tony Collins, chief executive of Virgin Trains - which is planning a three trains an hour service to Manchester and to Birmingham from December - said:  "We are satisfied  that, in  reaching its decision, the ORR has taken into account all the issues surrounding this very complex and challenging infrastructure project.  We welcome the ORR's statement that it will closely monitor delivery of the project.

"Obviously we respect the decision and we will do everything we possibly can to limit the inconvenience to customers during extensive works which will inevitably  cause disruption.  The test must be to ensure that the project is delivered  on time and can be maintained to a high standard so that the new timetable remains reliable."

Virgin said that among the initiatives to help passengers when the Rugby area is closed to trains where plans for: Extra carriages on East Midlands Trains between Liverpool and Sheffield via Manchester to help passengers travelling from North West England to London; re-design of the Virgin Trains website to make it easier to find out when and where engineering work is taking place; agreement for passengers holding Virgin Trains tickets to be able to travel from Manchester via Leeds to London using the services of Trans Pennine Express and National Express East Coast.

Freight company EWS said it was disappointed at the decision and said it would be meeting with ORR to gain a " full understanding over why this decision was made."

Graham Smith, EWS planning director, said:  "The West Coast main line is crucial for freight customers with 43 per cent of all freight trains operated each day using the route, all integrated into the supply chain of British industry.

"Whilst the Office of Rail Regulation is conscious of the adverse impact on rail freight their decision will have we need to understand how the ORR will protect freight during the enhancement works.  You can't put freight on rail replacement buses."