The Office of Rail Regulation today announced that Network Rail had complied with the order it made in February to produce a plan showing how it would complete the work on the West Coast main line to enable significant timetable improvements.
The ORR said Network Rail must now deliver its revised plan allowing the improvements to be introduced from December 2008.
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. We will closely monitor Network Rail's performance between now and December, ensuring that the new infrastructure operates reliably and is maintained safely."
Among the various improvements planned by train operators in the new timetable, Virgin plans to increase the number of trains an hour each way serving Birmingham and Manchester from London from the present two to three.
Tony Collins, chief executive of Virgin Trains, said today: "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."