Travellers heading home this Christmas will have to contend with disrupted services on a key London to Scotland rail route on December 23 and 24.
There will also be disruption to services on this West Coast route in the days after Christmas.
Part of a £125 million Bletchley resignalling project, the engineering work is part of planned works over the festive period. The work means there will be no direct services from Euston station in London to Milton Keynes, Birmingham, Manchester, Liverpool or Glasgow on December 23 and 24.
Hourly services will run from Euston via an alternative route (Chilterns) to Nuneaton where passengers will be able to change for services heading to all the destinations mentioned above.
Direct services resume on Thursday December 27, but with two of the four lines closed up to and including New Year's Eve. This means fewer (but direct) services to the usual destinations.
Network Rail (NR) network operations managing director Robin Gisby said: "Services on the West Coast on December 23 and 24 will be severely affected by a major project to increase line-speeds and capacity in the Milton Keynes area.
"We understand and regret the impact this will have on passengers and freight services, but believe it is unfortunately necessary to achieve the long-term benefits this work will deliver for many years to come."
NR and the Association of Train Operating Companies (Atoc) said that although there would be engineering work on the railways, the vast majority of people expected to travel over the Christmas and new year period should experience no disruption. They said the number of replacement bus services needed will be almost half that of the festive period last year.
Atoc chief executive Michael Roberts said: "A great deal of effort and planning goes into making sure that work to improve stations and make journeys faster and more reliable goes on while minimising disruption for our passengers.
"This year, we have again been able to reduce the number of people who will have to get on to a replacement bus. Once again train companies have been working closely with NR to make sure that we keep people on trains wherever we can."