Britain's second toll motorway is to be given the go-ahead by George Osborne later this year as part of a multi-billion pound road-building programme to stimulate the economy, The Independent has learnt.
The Chancellor will use this summer's Comprehensive Spending Review to revive a decade-old plan to underwrite a £1bn project to expand the M4 and ease congestion.
At the same time he is expected to give the go-ahead to a major upgrade of the A1, which will for the first time provide a continuous motorway or dual carriage way link between London and Scotland along the east coast.
Other projects under consideration include adding lanes to the A303 – known all too well to holidaymakers – which runs from Basingstoke through Somerset (past Stonehenge) to the south-west of England and to the A47, which runs through the Norfolk Broads.
In last month's budget Mr Osborne announced plans to increase the UK's spending on infrastructure projects by £3bn a year in an attempt to boost economic growth. "By investing in the economic arteries of this country, we will get growth flowing to every part of it," he said.
Details of which projects will get the cash are being negotiated between the Treasury and individual Government departments. But The Independent understands that several high-profile road schemes are likely to benefit.
These include funding guarantees for the construction of the new M4 relief road in South Wales. Under the proposals the Treasury would guarantee the borrowing costs for the Welsh government to pay for the scheme. The money would then be paid back through a toll on drivers.
The new 14-mile two-lane dual carriageway will run between junctions 23 and 29 of the M4 and is designed to end traffic bottlenecks at the Byrnglas Tunnels on the outskirts of Newport.
The plans were originally unveiled almost 10 years ago but were shelved five years later as costs rose to £1bn.
The project has a budget of £830m over 15 years and the Welsh government will be free to decide how much of that money it will seek to recoup through road tolls. Ministers believe the road will provide a significant boost to the South Wales economy. The extension has been backed by Welsh Conservatives.
Plans are also being considered to invest billions major road upgrades in England.
The single carriageway sections A1 between Newcastle and Berwick-upon-Tweed would be converted to dual carriageway, while there are also proposals to widen the A47 in Norfolk.
Funding is also likely to be secured for the A303 to be turned into a dual carriageway after a long-running campaign. The road is widely used by holidaymakers heading to the South of England and is heavily congested
Motoring groups welcomed the construction of a new motorway in Wales. However, environmentalists warned the road would cross the Gwent Levels, an area of unspoiled wetlands which provides habitat for otters, birds and rare plants. Sean Christian of the RSPB in Wales said it was a "very damaging development in an environmentally important area."
The RSBP has warned that the Welsh road would cross an unspoilt habitat for birds, otters and rare plants