The Government is considering the idea and is expected to announce next month that Britain may need a high-speed line to help to solve overcrowding on existing lines.

The new line, estimated to cost around £11 billion, would connect with the Channel Tunnel Rail Link just north of St Pancras station in London.

Passengers from Birmingham could catch Eurostar trains that bypass central London and arrive in Paris in three hours or Brussels in two hours and 45 minutes.

The plan was drawn up by Greengauge 21, a group of rail industry leaders, in response to the rapid growth in rail travel – up 50 per cent since privatisation a decade ago and up 10 per cent in the past year.

The Commons Public Accounts Committee gave warning last week that the West Coast Main Line would be full within eight years, despite an £8 billion upgrade.

The group said a new high-speed line would allow the existing route between London and Birmingham to take many more local and freight trains.

The line would have branches at either end: one towards Manchester and one to Heathrow, via a five-mile tunnel.

The line could eventually be extended all the way to Manchester but, to reduce early costs, would initially connect with the existing line about 20 miles north of Birmingham.

Even with part of the journey limited to 125mph on the existing line, the journey time between London and Manchester would fall from two hours and 10 minutes to 90 minutes.

Jim Steer, director of Greengauge 21 and former head of strategy at the Strategic Rail Authority, said the line would eliminate the need to continue the 30 flights a day between Heathrow and Manchester.

The line, which would take up to 15 years to plan and build, would be designed to take double-deck trains like those on French high-speed lines.

It would have a capacity of 16,000 seats an hour between London and Birmingham and a large proportion of the passengers would previously have driven between the two cities.

Mr Steer admitted that the new line would encourage some people to commute longer distances and to make extra journeys, undermining its environmental benefits.

He said the Government would have to fund part of the cost of the line but was unable to say what proportion.

The proposed route would largely use spare land beside existing tracks to reduce the cost and minimise the impact on the green belt and the amount of land needing to be compulsorily purchased.

Mr Steer said: “Piecemeal solutions are an addiction which we need to break free from because they end up being more costly than investing for the long term.

“High-speed rail is the critical step needed to support a growing economy in a sustainable way.”

Projects on and off track

— Thameslink 2000 upgrade of the north-south route across the Thames.

Cost £3.5 billion

Completion date 2015 (est)

Status has planning permission and the Government is likely soon to approve the funding

— Crossrail main line rail tunnels running east-west under London, linking Heathrow with Canary Wharf

Cost £16 billion

Completion date 2018 (est)

Status planning Bill going through Parliament. Treasury not yet convinced but may approve first stage this year

— East Coast Mainline upgrade remove bottlenecks on route between London Kings Cross and Edinburgh

Cost £3billion

Completion date uncertain

Status original plan diluted