Rail passengers planning to travel over the Christmas period may be forced to do so earlier than planned as over 200 sets of engineering works were announced.
Many of Britain's mainline routes will be partially shut during the festive period as Network Rail carries out its biggest ever Christmas investment programme.
Some 260 schemes will be completed by 32,600 workers.
However, Network Rail - controller of the UK's railways - say more than 95% of the network will be unaffected by the work.
Great Western Railway advised passengers to complete journeys by December 23 "at the latest" as London Paddington will be closed between Christmas Eve and December 27.
The London end of the Great Eastern main line will be suspended from December 23 to New Year's Day, meaning there will be no Greater Anglia trains between London Liverpool Street and Ingatestone or Billericay.
The West Coast main line will be halted between Preston and Lancaster from December 24 to 27, with buses replacing trains.
Passengers travelling between London and Glasgow during this time are advised to go via Edinburgh, adding around an hour to journeys.
Southeastern, which serves London, Kent and East Sussex, will not be able to run trains to London Bridge, Charing Cross and Cannon Street between December 23 and January 1.
Network Rail's chief executive Mark Carne said: "While most of the network is open for business as usual, some routes are heavily affected and so we strongly advise passengers to plan ahead this Christmas.
"We know that our railway is up to 50% quieter than usual during the festive period so taking on and delivering these huge transformational schemes at this time of year minimises our impact on passengers."
He added that many passengers are on the cusp of seeing their journeys "transformed" with thousands of new services "just around the corner".