Tycoon Sir Richard Branson once said the goal of his Virgin rail business was to grass over Britain's motorways.

With this week's announcement by Network Rail that it was launching a study into the prospects for new railways in England - including the Great Western Main Line and Chiltern Line corridors through Oxfordshire - the Kidlington businessman's dream may be a step closer.

While Network Rail's key concern is creating extra capacity to cope with rising use of the rail system, it raised the prospect of building new lines, similar to High Speed 1, the route linking London St Pancras and the Channel Tunnel, opened last November.

Chief executive Iain Coucher said: "By 2025 many lines will be full up, especially those running to and from the north and west of London. This will happen even after we have implemented the investment to boost current capacity.

"With popularity for rail growing, we have to start planning for the medium and long-term future today.

"We have to see how we can meet the capacity challenge and see what solutions - including potentially, that of new lines - are deliverable and affordable."

Anyone travelling on a Eurostar train between London and Paris gets a preview of how the M40 and M4 could look in the future, if Britain begins to build new lines like those created for France's TGV trains and Germany's ICE.

For much of the journey between Lille and Paris, Eurostars run alongside the A1 motorway, on which lorries make up the bulk of the traffic.

Cars and planes cannot compete, on journey times or cost, with the fast, frequent trains on the parallel rail route, running at 186mph (300kmh).

In Britain about 30 flights a day continue to crowd the skies between London and Manchester, to give but one example.

Greengauge 21, a grouping of leading figures in the rail industry, which has been developing its own plans for a high-speed line between London, the West Midlands and the North West, running along the Chiltern Line/M40 corridor, says any new high-speed network must have a station at London's Heathrow airport.

It says this would encourage a substantial transfer from domestic and short-haul European flights to trains.

Greengauge 21 director Jim Steer, while welcoming Network Rail's study, said: "We will be looking at the wider benefits that high-speed rail can bring, and not just the rail network capacity concerns.

"The wider case for new high-speed lines requires an examination across the transport modes - otherwise the clear carbon reduction benefits can be missed - and also requires looking at sustainable development and economic regeneration."

These benefits will be critical in building a case for high-speed rail, because such lines are expensive.

The 68 miles of High Speed 1 cost £5bn, although this figure was inflated by costly tunnels needed to carry the line under East London.

Long-distance passengers would be the big winners, but new high-speed tracks through Oxfordshire also hold out the prospect of slashing commuter journey times.

Greengauge proposes a high-speed branch line to Oxford, also serving Bicester, which could see journey times of about 30 minutes to the capital and free up capacity on the existing Chiltern and Great Western routes.

Commuter services could be similar to those that will be provided for passengers from Kent next year, when 140mph Class 395 electric trains, built by Hitachi of Japan, will cut journey times between Ashford and London from 83 minutes now to just 36.

Though this will come at a cost - fares will be 20 per cent higher than on traditional services.

For more details of Greengauge 21's high-speed route plans, see www.greengauge21.net