All trains in and out of London King’s Cross are cancelled because of overrunning Network Rail engineering works north of the station, with a reduced service running tomorrow.
The advice to defer travel if possible comes as many workers who travelled to see relatives over the festive period are expected to use the railways to return to work on Monday.
East Coast spokesman Paul Emberley said: “Network Rail has apologised to passengers for the inevitable delays to their travel plans on Saturday as a result of the overrunning engineering works.
“East Coast is particularly sorry too for the inconvenience to its customers as a result, on what we know is an already very busy travel day immediately following the Christmas break.
“For customers intending to start or finish their journey at King’s Cross, consideration should be given to deferring travel plans to either Sunday or Monday.
“We’re working hard over the holiday period to make the necessary adjustments to our timetable as a consequence, and to provide as much information as we can.”
Network Rail said that the work was part of a £200 million Christmas investment programme, with most railways expected to return to normal on January 5.
It is one of 300 projects being undertaken over the holidays across 2,000 sites up and down the country by some 11,000 railway engineers.
A spokesman said: “What has happened is really regrettable and unfortunate, but it is a small part of a massive amount of engineering investment taking place over Christmas.”
The spokesman said that on a normal day 4.5 million passengers use the railways on average every day, compared with two million a day over the holidays.
David Sidebottom, passenger director at the independent watchdog Passenger Focus, said: “Investment in maintenance and improvement is necessary, and we passengers understand that.
“But overrunning works that disrupt already-limited festive travel are frustrating.
“Our research is clear: passengers want to be kept on the train wherever possible, they want to know before buying a ticket if part of the journey will be by bus, and they want plenty of staff on hand to signpost where to go and what to do.
“We will be looking to see that operators and Network Rail are doing all in their power to alert passengers, to help them make alternative arrangements and to make it easy for them to claim refunds or compensation.”
East Coast said customers who had been intending to use King’s Cross would need to start or finish their journey tomorrow at Finsbury Park in north London, with at least once change of train.
Sunday’s reduced service will see trains leaving King’s Cross up to 20 minutes earlier than normal and resume their usual stopping times from Peterborough onwards.
Services to King’s Cross will arrive up to 40 minutes later than normal.
Other services will start or end at Doncaster, Newark North Gate, Peterborough or Stevenage.
A Department for Transport spokesman said: “It is extremely disappointing that Network Rail’s engineering works have overrun and will affect travellers during this festive season, passengers will be rightly annoyed.
“This was essential work but passengers need to be able to plan and rely on Network Rail meeting its deadlines for having the network back in service.
“The department is in contact with Network Rail to understand what went wrong and if lessons can be learned for the future.”