Their report for the government says the extra lanes are needed over a 50-mile stretch.

The findings have been condemned by the environment group, Friends of the Earth.

Spokesman Chris Crean said: "We defeated the great Thatcher road building in the 1990s, but these multi-modal studies are bringing them back again."

Traffic nightmares

He predicted the widening would not help ease traffic congestion in Greater Manchester, the West Midlands or in towns along the motorway such as Crewe, Stoke and Stafford.

"It will probably increase traffic demand in these cities, which are already choked with traffic," he said.

The stretch earmarked for widening runs mainly through Staffordshire and Cheshire.

The report also recommends additional rail services from Birmingham to Manchester, increased freight capacity, the re-opening of the Sandbach to Northwich rail line, and tolls on the M6 sometime after 2021.

The M6's junction 20 would also be made fully directional with new slip roads from the M56 in the east and to the M6 in the south.

A spokeswoman for the Government Office for the West Midlands said the proposals were not final, and would be sent to a steering group and finally to the two regional planning bodies involved.