Millions of rail passengers suffered delays, disruption and above-inflation fare rises on Wednesday as they made a bleak return to work after the Christmas break.

Part of one of the busiest north-south rail lines was closed after engineering work took longer than expected and London's busy Liverpool Street was also closed for demolition work.

Network Rail said the West Coast Mainline around the Rugby area would remain closed on Thursday for repairs, disrupting thousands of journeys.

"The scale and complexity of what was there has certainly taken us by surprise," its customer services director Robin Gisby told BBC radio. "It is certainly going to be shut for at least another day."

The Office of Rail Regulation has launched an investigation into the delays. No date has been set for the end of the works.

Rail watchdog Passenger Focus said the industry must do all it can to avoid a similar incident in the future.

"Passengers are paying more but the rail industry must keep its side of the bargain by keeping its promises on engineering work," its Chief Executive Anthony Smith said. "Telling people not to travel on a working day is an extraordinary message."

Virgin Trains, which operates between London and the northwest, advised people not to travel on its services.

Liverpool Street station, one of the capital's main commuter stations from Essex, was closed after the demolition of an old bridge was not finished on time.

Train operators said the cost of most season tickets will climb by an average of 4.8 percent, while other fares such as cheap day returns will rise by 5.4 percent.

Passenger groups said the fare hikes would send a "chill wind" down platforms, but rail bosses said the money would help pay for new trains, better service and station upgrades.

"Billions of pounds are now being spent to improve the railway and the results are showing through," said George Muir, head of the Association of Train Operating Companies.

Higher ticket prices will shift the burden of paying for the railways from taxpayers to passengers, in line with government policy, he added.

However, Passenger Focus's Smith said people using many commuter routes face higher price hikes than the average.

"Steep rises on individual routes are masked by the average figures published by the industry," he said. "A chill wind will blow down many of Britain's platforms when passengers find out their new fares."

For example, an annual ticket from Gillingham in Kent to London will cost 2,740 pounds in 2008, compared to 2,496 pounds last year -- a rise of 9.78 percent.

Lobby group Campaign for Better Transport, formerly Transport 2000, said higher fares would encourage people to drive rather than take the train.