Vital investment which would allow more trains to run between King's Lynn and London, and from East Anglia into the Midlands, could be delayed amid a review called by the Department for Transport.

South-West Norfolk MP Elizabeth Truss has raised concerns that work to the Ely North junction may not be finished by 2017, as previously planned, as a result of the study being conducted by government-funded rail infrastructure body Network Rail,

She has written to rail minister Claire Perry to request a meeting to seek assurances that the brakes will not be slammed on the project.

Network Rail has been told to review all of its projects planned between now and 2019 – the timeline known as control period five – by the Department for Transport, raising fears that previously agreed projects could be delayed.

A Network Rail spokesman said: 'When we have the results of that review we will be able to provide further information about the Ely North Junction upgrade.'

Ms Truss said: 'Upgrading the Ely North junction will allow for half-hourly services on the Downham Market route and increased services on the Thetford line.

'Cross-country and freight services also significantly benefit from this vital upgrade and I am keen to ensure the timetable is kept on track.

'I understand that just prior to the election the Department for Transport instigated a review of all works in the CP5 schedule and I want reassurance that this will not create delays on the key rail routes in our region. This is an issue I have been campaigning for over the last four years and I have asked for a meeting with the rail minister Claire Perry.

'With rail passenger numbers increasing each year, the economic value of the upgrade to my South-West Norfolk constituency and the county as a whole is absolutely clear and this is the message I will continue to make to the Department for Transport.'