Britain will consider building five new main rail lines in a strategic review that could lead to the biggest railway expansion in more than a century to try to cope with booming demand, Network Rail said on Saturday.

The railway infrastructure operator will commission a study to look at ways of increasing capacity by 2025 when the existing main lines are expected to be full up.

With passenger numbers at a 60-year high, fuel prices rising and environmental concerns about planes and cars growing, it is time to "make a case for expanding the rail network", a spokesman said.

"All solutions are going to be on the table," he said. "Having new lines is the premise we are going to test because they free up capacity on the existing lines."

New routes could be built alongside existing tracks, the spokesman said. The cost would run into many billions of pounds, although no estimates of the budget were released.

The Network Rail spokesman said the bill would be "very high", but added: "You've got to look at the wider benefits. It would drive growth to the economy and get people out of cars and domestic airliners."

The high-speed link between London's St Pancras station and the Channel Tunnel is the only major new line to be built in Britain in the last century, at a cost of 5.8 billion pounds.

The study, due to begin later this summer, will also consider whether to construct high-speed lines to provide a service similar to France's TGV.

It will examine five of the busiest routes, including the west coast main line, which links London with Birmingham, Manchester, Liverpool and Glasgow, and the east coast main line between London and Scotland.

Network Rail has invited consultants to bid to conduct the review, expected to be completed by summer 2009. Full details of the study will be announced on Monday.

The company took over the rail network from the failed Railtrack Plc in 2002. It has been battling to turn around a rail system which suffered from years of under-investment as well as a history of accidents and escalating costs.

Despite rising passenger numbers, campaign groups have complained about increasing fares and delays in recent years.