Rail passengers hoping to visit loved-ones over Christmas are being urged to book “as early as possible” to avoid travel chaos.
London North Eastern Railway (LNER) issued the warning as it prepares to release its tickets for the festive period on Friday.
The operator, which runs trains between London King’s Cross and Scotland, expects its Christmas Eve services to be swiftly snapped up.
It is running with “substantially reduced” capacity in its carriages to enable social distancing, and anyone who has not pre-booked tickets will be prevented from boarding.
King’s Cross station will be closed for six days from Christmas Day as part of the £1.2 billion upgrade of the East Coast Main Line.
An LNER spokesman said: “We understand the disruption this engineering work may cause to Christmas plans this year, so we are urging our customers to plan and book their travel as early as possible.”
More than 2.2 million people normally use trains to get home between Christmas and New Year, many of them travelling from or through the capital.
This week Londoners hit out at the “absurd” prices of Christmas train travel and said they were facing “travel chaos” amid ongoing coronavirus restrictions.
On Tuesday, Transport Secretary Grant Shapps said people should consider not travelling by train at Christmas.
He told BBC Breakfast: “We have got to understand there are limitations to the (rail) network caused by, for example, things like the need on some trains to pre-book tickets at this time, in order to prevent overcrowding.
“So we are going to be appealing to people to look very carefully at the transport route they take and of course even making a choice about whether they travel at all.”
Avanti West Coast, which operates trains on the West Coast Main Line, is releasing its Advance fares in the coming days.
These cheaper tickets are usually available 12 weeks in advance, but their release has been delayed during the pandemic due to short-notice timetable changes.
Rail regulator the Office of Rail and Road last month said companies must do more to keep travellers informed.
However, the alternatives are not looking much more promising, with National Express yet to release most of its popular coach services for December.
Passengers hoping to travel from Victoria have been unable to book for destinations such as Darlington, Durham and Newcastle over the Christmas week.
Shadow Transport Secretary Jim McMahon said of the issues: "It’s imperative the Government quickly produces a fully worked through transport plan to ensure we don’t see Christmas travel chaos on our roads and trains where staff and passengers are kept safe, with capacity on the rail network to meet demand."