Building new London to Scotland high-speed rail lines could be worth more than £60 billion to the UK economy, a report from planning and engineering consultants Atkins has said.
But the lines - one going up the east coast, the other up the west coast - would probably not be operational before 2026, the report said.
Building two new lines, which would stretch as far north as Glasgow and Edinburgh, would give the best economic benefit, the report concluded.
Atkins said that the cost of the lines would be about £31 billion but that they would deliver £63 billion worth of economic benefits over the first 60 years.
London to Birmingham journey times could come down to just one hour while London to Glasgow could take just three hours.
Examples of other journey times include London-Wolverhampton 76 minutes, London-Sheffield 80 minutes, London-Leeds 86 minutes London-Manchester 74-79 minutes and London-Liverpool 96 minutes.
Atkins said that the lines would be necessary as capacity on existing lines could be exhausted quicker than expected - perhaps within a decade.
Atkins transport planning managing director Andy Southern said: "It is clear that a high speed rail network should not only be viewed in terms of its benefit to relieving congestion on the rail network. The economic gain could also be extremely significant.
"Our modelling shows the impact would be felt by local communities as well as the business traveller choosing to go by rail rather than air. There is also potential to reduce overall carbon emissions from transport in the UK."
