People should consider not travelling by train at Christmas due to the rail network's "limitations", Transport Secretary Grants Shapps has said.
The Westminster Government and the devolved administrations are expected to announce later this week how coronavirus restrictions will be eased to allow people across the UK to spend the festive period together.
But with major engineering work across Britain's railways and capacity constraints to enable social distancing, Mr Shapps urged people to "look very carefully at the transport route they take" when planning Christmas trips.
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.
"It is the reality of the situation we're in; we will try to do everything we can with the network to make it as good as possible, but I think it is worth people being aware that busy times of travel is a problem."
He added that he is in "close contact" with transport leaders of the devolved governments to make Christmas travel plans, which he expects will be finalised "later this week".
Engineering work will be carried out by Network Rail from December 23 to January 4.
Projects include track renewals, bridge replacements and improvements to signalling and overhead line equipment.
Most of the railway will stay open, but some lines will be closed to allow the work to take place.
London King's Cross station will be closed for six days from Christmas Day as a £1.2 billion upgrade of the East Coast Main Line continues.
London North Eastern Railway is warning that "alternative routes will likely be very busy and should also be avoided".
The operator, which runs trains between the capital and Scotland, is also telling passengers to "avoid travel" on Christmas Eve and December 31 to January 3 because "services will be very busy with reduced capacity".
Network Rail said there will be a "significantly reduced service" at the UK's busiest railway station – London Waterloo – between Christmas Day and January 3.
This is to enable work to be carried out on lines approaching the station in a bid to improve punctuality.
Vauxhall and Queenstown Road stations will be closed over the period as part of the project.
The installation of a new signal gantry will disrupt services through Bristol Temple Meads from December 27 until January 10.
Passengers are advised to check journey details before travelling.