Thousands of passengers who have booked train journeys on New Year’s Eve will endure long delays and have to catch buses after Network Rail announced that it had miscalculated how long it would take to complete engineering works.

The overrun of the works will mean that Britain’s busiest line, the West Coast Main Line, will be severely disrupted as people return to work or travel to join relatives and friends for new year parties.

Virgin Trains accused Network Rail of incompetence and bullying, saying that the company was abusing its monopoly over rail infrastructure. Network Rail is supposed to give at least 12 weeks’ notice of line closures but revealed only yesterday that it needed the extra day.

The line was already due to be closed at Rugby on December 27, 28, 29 and 30 and the closure will be extended to include the whole of December 31, so the first through trains after Christmas from Glasgow, Liverpool, Manchester and Birmingham to London will not run until January 1. Passengers will have to disembark at Birmingham International and catch a bus to Northampton, where they will catch another train, adding at least an hour to the journey.

Virgin has complained to the Office of Rail Regulation, which is investigating and could fine Network Rail for breaching its legal requirement to give proper notice of works.

Chris Gibb, managing director of Virgin Trains, said: “We simply cannot have NR [Network Rail] bullying train operators in this way just because their engineering planning processes are in a mess.”

Virgin said that the overrun of the works would affect at least 50,000 people planning to travel on New Year’s Eve, including 6,000 who had already bought tickets.

Anthony Smith, chief executive of the rail watchdog Passenger Focus, said: “This is unbelievable. Thousands of passengers have booked or planned new year travel in good faith. We feel very let down and want reassurances that the huge amount of engineering work planned for next year will not run into similar problems.

Network Rail’s decision to close several key lines over Christmas contrasts starkly with the policy of the Highways Agency, which is completing or suspending two thirds of its roadworks on motorways and A roads in England in time for the beginning of the big getaway tomorrow.

There will be replacement buses on the East Coast Main Line between Hatfield and Peterborough on December 23 and 24, affecting passengers from London King’s Cross.

London Liverpool Street station will be closed from December 23 to January 1 inclusive, affecting passengers on One’s services across East Anglia. There will also be engineering work between December 23 and January 1 inclusive between Brentwood, Ingates-tone and Billericay.

TSSA, the white-collar rail union, claimed yesterday that rail companies were trying to maximise profits by restricting the number of cheaper book-ahead tickets available over the Christmas holidays. The union said it believed that less than 10 per cent of the people travelling on the busiest routes would have purchased a cheaper ticket. Gerry Doherty, the union’s general secretary, has written to Ruth Kelly, the Transport Secretary, urging her to instruct the rail companies to publish the exact percentage of cheaper seats that are available in advance.

He said: “Many people trying to book on line are finding these so-called deals are a mirage. The truth is no one knows how many cheaper seats are being sold because the rail companies will not tell us.”

At 3pm tomorrow up to 18 million drivers, burning the country’s most expensive petrol yet, will be on the road Another four million will be on the trains.

The numbers will be boosted this year by the falling of Christmas Day and New Year’s Day on Tuesdays. Offices are not expected to reopen on the Mondays, meaning that many will be off until at least January 2.

Up to three million are predicted to be flying abroad, with the Canary Islands and Florida the top destinations.

For those at home, only four million vehicles are expected on Christmas Day roads. The number will rise sharply afterwards, with up to 16 million on both December 27 and 28. The RAC, however, found that nearly six out of ten drivers said that they were less likely to travel this year because of the price of fuel.

The congestion hotspots tomorrow will be: M25; M1 from junctions 6a to 10, and junctions 20 to 30; M4 west between J1 and J11, and J19 and J21; M6 from J4 to J10 in both directions; M60; M62 in both directions between J23 and J30; M8.

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