Doubts have been raised about the completion date for flagship plans to electrify the trans-Pennine rail route.
Ballooning costs and delays to electrification plans on other routes including the mainline between London and Sheffield are said to be behind the slippage, according to industry sources.
Delays would be an embarrassment for Chancellor George Osborne, who has backed plans for the route linking Liverpool, Manchester, Leeds and York.
Network Rail has previously said electrification will be finished by December 2018. But there is speculation this could be shunted back up to three years.
Last night Network Rail said: “The programme is undergoing detailed development that will allow the project to fully understand the work needed and the cost involved to deliver the agreed benefits for passengers. The results of this work are expected in the spring.”
The Department for Transport said: “Network Rail continues to develop, design and cost the electrification programme with both the department and Office of Rail Regulation. The Transport Secretary has been clear this project should be delivered within the overall Network Rail budget.”