Great Western Railways has issued advice ahead of an increase in travel and potential disruption during the Christmas period.
GWR has announced there are no planned alterations before Christmas day, but there will be significant changes between December 27 and December 29.
After Christmas Eve, no main line trains will run to or from London Paddington until Monday, December 30.
Most of GWR’s long-distance services will start from or terminate at Reading, where customers will be able to pick up connecting trains to Ealing Broadway from where London Underground services run into central London.
Those travelling from South Wales, Devon or Cornwall will however each have an hourly service diverted into London Euston instead. These trains will not stop at Reading.
To help keep customers comfortable and minimise crowding, these trains will be on reservation only, so make sure you book beforehand.
GWR operations director Richard Rowland said: “This is a really complex operation, and we have worked hard to make sure people get to where they want to.
"We will run an hourly service from the south-west of England – Cornwall, Devon – and an hourly service from South Wales which will go into Euston.
“We will then have several trains which will terminate at Reading, and people can connect there, and we will also have trains to Ealing Broadway for those making more local journeys.
"It is really important to us that we can keep customers moving and get them to where they need to go this Christmas. One of the reasons we chose Euston was that its most convenient for many of our customers who are making journeys beyond West London.
Network Rail Western route director, Marcus Jones explains: "Our festive upgrades ensure the railway runs reliably and safely.
"We appreciate there is never a good time to disrupt journeys but whenever possible we do this at times when fewer people are travelling, such as at Christmas, on bank holidays or at weekends.
"We thank passengers in advance for their patience and urge them to please check before they travel.”
Work will also affect services through Westbury from December 27 to January 23. The railway between Westbury and Salisbury and through Westbury station will be closed to enable track upgrades.
Trains will be diverted or replaced by buses.
Passengers are advised to check their journeys before travelling and to plan well in advance. More information can be found at www.GWR.com/Christmas.