Train passengers heading to London from Birmingham New Street are being warned to check the timetable today before travelling.
Network Rail is carrying out improvement works at London Euston, forcing it to shut some railway lines.
Virgin Trains says that means services to and from the English capital will be reduced, with with two per hour today between Euston and the West Midlands.
Birmingham New Street also tweeted out advice to rail passengers saying there would be a reduced service today for passengers.
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Birmingham New Street tweeted: "Trains resume today and are running an amended train service with a reduced frequency also on some services.
"Services are expected to be extremely busy across all services today as first day after Christmas.
"Please plan ahead and allow extra time to complete your journey."