Proposals for a new Birmingham to Manchester toll road were thrown into turmoil today after they were rejected by a House of Commons inquiry.

MPs attacked controversial plans for the 50-mile motorway, the centrepiece of the Government's transport policy for the Midlands and North of England.

It followed the Department for Transport's decision last year to put long-awaited plans to widen the existing M6 on the back burner.

Transport Secretary Alistair Darling revealed he was instead considering a new toll motorway, to be called the M6 Expressway.

Mr Darling justified the change of policy by claiming the M6 Toll, which runs for 27 miles north of Birmingham, had proved that toll roads could be a success.

But the Transport Select Committee, led by senior Labour backbencher Gwyneth Dunwoody, poured scorn on the claim in a scathing report yesterday.

The MPs said their inquiry had found there was no reliable evidence to demonstrate whether the M6 Toll was a success or not. It might actually have damaged the West Midland economy, they said.

The Government's focus on building a toll motorway meant other much-needed improvements to the region's transport system were under threat.

And the public consultation on the proposed toll road launched last July had been rendered meaningless by a failure to provide clear details of the scheme, they warned.

The inquiry was told the West Midlands may have been placed at an economic disadvantage because it was the only part of Britain with a toll motorway, the MPs said.

They warned: "We are concerned that evaluation to date has been limited to traffic flows, with no systematic attempt by the Government to assess the economic and safety impacts of the new road."

But despite this, the Government had decided to suspend plans to widen the existing M6.

"We are concerned that early data from the M6 Toll road are being used to justify the consideration of a second tolled motorway north of Birmingham to Manchester."

They rejected on the Government's proposed timetable for building a new motorway.

"We find it hard to believe the Expressway could be built and open by 2016," they said.

But the decision to consider a new toll road "suggests that improvements in the region will now be delayed," the MPs said.

It could even threaten long-awaited improvements to the rail network, they warned.

"The regional transport representatives pointed to other transport projects that, given funding, would better serve the community.

"The provision of high quality motorways between the West Midlands and the North-west will affect people's choice of whether to travel by car or rail."

They added: "The Department [for Transport] must provide more detailed information in its consultation document in the future if it expects the public to submit meaningful comments."

The Department for Transport defended the Expressway plans yesterday.

A spokesman said: "The consultation documents on the Expressway were detailing a broad concept, not a firm plan.

"We wanted to explore the idea of having an Expressway as a pose to widening the M6, which is the other alternative.

"It was not a detailed consultation on the plan, because there is not one in place yet."