Rail passengers travelling to and from London over the Christmas period face major disruption as lines close for engineering work.
Network Rail said major infrastructure works are being carried out during the festive period.
Work on some schemes will begin on Christmas Eve - which falls on a Saturday - to give engineers and maintenance teams four days to carry out upgrades before the next working day.
In London, no trains will operate to or from London Paddington between December 24 and December 29 because of work to build the new Crossrail rail link.
That means the Heathrow Express service between Heathrow Airport and Paddington will be suspended for six days and Great Western Railway trains will terminate at Ealing Broadway.
Major upgrades of signalling, track and overhead lines for Crossrail's eastern section mean bus replacements and diversions will be in place for services to and from London Liverpool Street from December 24 to January 2.
Work at New Cross, south London as part of the Thameslink programme means no Southeastern trains will operate to London Bridge and Charing Cross from December 24-28, apart from the Hastings services which will be diverted to London Bridge.
Phil Hufton, NR's managing director for England and Wales, said engineering work is carried out throughout the year but larger upgrades usually take place over bank holidays as up to 50 per cent fewer passengers travel on those days.
He added: "Despite our essential upgrades, the vast majority of the rail network - more than 95 per cent - remains unaffected and will be open for business as usual.
"This vital investment will make the railway more reliable for years to come, while improving journeys for thousands of passengers.
"There's never a good time to impact on journeys and I'd like to thank passengers in advance for their patience."
