Evening services from Cambridge to Ely and King’s Lynn will end earlier than scheduled to allow for urgent repairs to the line.
The decision was taken Network Rail and GTR to close the line early at 20.45 each weekday evening, Mondays to Fridays, up to and including Tuesday October 4.
The early closures begin on Monday September 26.
Network Rail says the work is needed to “repair track defects caused by the recent heatwave”.
A spokesperson said: “The earlier prolonged spell of dry weather has caused the peaty ground beneath the track along the Fen Line between Cambridge and King’s Lynn to shrink, affecting the track above.
“Network Rail has introduced speed restrictions to allow a rail service to run safely and to prevent further damage to the track.
“Engineers have been realigning the track over the last four weeks which has enabled speed restrictions to be removed in some areas but not enough to run the full timetable reliably.”
The spokesperson added: “In order to complete the work as quickly as possible, and minimise disruption to passengers, a decision has been taken jointly by Network Rail and GTR that the line will close early at 20:45 each weekday evening, Mondays to Fridays up to and including Tuesday 4 October.”
Last trains will run from King’s Lynn and Ely around 20:00.
The expectation is this will remove the worst speed restrictions and restore normal through services from King’s Lynn to London from Wednesday 5 October, although this will be subject to final checks.
Further updates will be provided next week.
Ellie Burrows, Network Rail’s route director for Anglia, said: “We recognise the impact this is having on passengers, so this remedial work is being carried out as a priority.
“The early closure of the line will help to speed up this work. I am very sorry for the delays and thank passengers for their patience while we carry out these repairs.”
Jenny Saunders, customer services director for Great Northern and Thameslink, said: “We’re sorry for the continued changes we’re having to make to our rail service between Kings Lynn, Cambridge and London but it is absolutely essential to ensure the continued safe running of our trains and to give our customers a dependable service.
“We’ll continue not running some of our trains between London and Cambridge or Ely in the meantime, which will make other services busier, and passengers for stations along the route to King’s Lynn will have to continue changing at Cambridge until the direct service can be restored.”
For more information, passengers should see www.greatnorthernrail.com or www.nationalrail.co.uk