Five new high-speed main lines crossing the length and breadth of the UK may be built as part of a review of the rail network, Network Rail says.
The network operator will announce on Monday it is to commission a study looking into what could be the largest track build since the 19th Century.
The study will consider laying new lines alongside five of the UK's busiest routes by 2025.
They include the East Coast main line and West Coast main line.
The review will also assess the need for high-speed trains similar to the French TGV to cope with Britain's growing number of rail users.
In the past decade, passenger numbers have risen by about 40% with more people travelling by rail than at any time since 1946.
In addition, numbers are expected to swell by a further 30% in the next 10 years.
The study being commissioned by Network Rail will look at the service in the post-2014 period, with all options "on the table".
If given the go-ahead, the new lines are likely to run alongside some of the UK's busiest existing routes to and from London.
They include the West Coast line to Birmingham, Manchester and Glasgow, the East Coast main line to Edinburgh, the Great Western main line to Cardiff and Penzance, the Midland main line to Sheffield and the Chiltern route to Birmingham.
A spokesman for Network Rail said: "We are looking at these five strategic routes. We are possibly looking at new lines.
"There is a huge case to be made for an expansion of the rail network. All options are on the table looking at how we address capacity issues."
Richard Dyer, transport campaigner at Friends of the Earth, said: "Expanding Britain's railways by building new high speed lines is potentially very exciting - and could play an important role in weaning Britain off fossil fuels and developing a low carbon economy.
"But the overall impact that this would have on local people and the environment must be carefully considered.
"The UK needs a modern, comprehensive and affordable rail network to provide a real alternative to cars, lorries and short haul flights, and help cut Britain's contribution to global climate change.
"Our creaking railway system desperately requires huge investment to bring it into the 21st century."
Ashwin Kumar, passenger director of independent watchdog for rail users Passenger Focus, said: "We welcome the study. It is extremely important the rail industry anticipates future growth."