Sections of three main rail lines across the east are to close for engineering works over Easter, threatening disruption to travellers.
Replacement buses will fill gaps in local services
Parts of the West Coast Main Line through Hertfordshire and Northamptonshire will close on all four days of the holiday.
Replacement buses will be running in Essex because of work affecting trains between Norwich, Ipswich and London.
Timetables will change on the Kettering to Bedford and Cambridge to Ely lines.
On Good Friday, buses will replace Virgin Trains services between Northampton and Birmingham.
At the same time in Essex, buses will replace services passing through Brentwood.
From Saturday, the Northampton to London line will shut and timetables will be disrupted between Bedford and Kettering.
From Sunday, the line from Cambridge to Ely will close along with Liverpool Street to Brentwood plus the Clacton and Walton branches in Essex.
Services should return to normal on Tuesday but Virgin Trains is already warning there may be fewer trains.
Network Rail said the work is being carried out over Easter because that is the time when fewer people are travelling.
They are assuring passengers work will complete on time despite over 30 projects under way across Britain with more than 6,000 people working around 300,000 man-hours over the Easter weekend.
"We are making all sorts of improvements including laying new track, repairing bridges and updating signalling systems," the company said.