Revised timetables will kick in on the Northampton rail line this week and next.
Amended timetables will be in place from Tuesday 24 December until Wednesday 1 January 2020, with a reduced service on some routes on London Northwestern Railway.
Network Rail will also be carrying out planned improvement works at locations across the network during this period.
The train operators are advising customers to plan ahead and allow plenty of time for their journeys, as services are likely to be busier than usual.
Andy Camp, commercial director at London Northwestern Railway, said: “A lot of people will be travelling over Christmas and New Year and we want everyone to get where they need to be as smoothly as possible.
"We advise our passengers to leave plenty of time to make their journey and to check their train times before setting out. We don’t want anyone to get caught out by amended timetables or to miss their last train home.”
On Christmas Eve, reduced timetables will operate on some routes from 3pm onwards, with services finishing earlier than usual. The last trains from towns and cities are often very busy, so passengers are advised to travel earlier in the day wherever possible.
As usual there will be no trains operating on Christmas Day or Boxing Day. Services will then resume slightly later than normal on Friday 27 December.
Planned improvement works are taking place at some locations between Friday 27 December until Wednesday 1 January 2020, affecting services across the network.
Revised timetables will be in operation on December 27, December 30 and New Year's Eve on London Northwestern Railway services between London Euston and Watford Junction, Tring, Milton Keynes Central and Northampton.
Buses will replace trains between Milton Keynes Central and Northampton/Rugby after 9.30pm on Monday 30 December.
For the latest travel updates over the festive period follow @lnrailway and @westmidrailway on Twitter