The Tories have denied Liberal Democrat claims that they were planning to charge £10 a month for drivers to use the A47.

Norman Baker, who was a transport minister in the last Government said his coalition partners had drawn up a document looking a levy or 'vignette system' where motorists would have had to buy a 'network pass' to use the road. Mr Baker claims the plans were pushed by George Osborne as a way of generating extra revenue.

But Transport Secretary Patrick McLoughlin said: 'This is nonsense cooked up by desperate political opponents. There are no plans to toll this or any other road. The Conservatives are committed to making significant improvements to the A47. Only a Conservative government could continue the record levels of investment in our infrastructure started in the last parliament, helping people to get on with their daily business.'

The plans were looked into as part of a broader study looking at the future of the roads, but the Liberal Democrats claim they blocked them when they saw the detail.

The plans would have included a lot of A-roads, as analysis showed that a lot less people would choose to pay for just motorways – DfT and HMT thought the network would need to cover up to 85pc of the roads network, and a new network of cameras with automatic numberplate recognition would have caught any drivers using the trunk roads without having paid up.

He claims the A47 was among the roads that would have been included, along with the A428 in Cambridgeshire,

Mr Baker said he had strongly opposed it on environmental grounds.

'At the moment, drivers pay tax according to how much carbon dioxide their car pumps out, which is entirely right. As cars have become more environmentally friendly, and families have started buying smaller, greener cars and are taxed less, the flow of money going to the Treasury is drying up.

'The Tory proposal would have broken the 'polluter pays' link that we have at the moment between emissions and tax, by charging a flat amount for accessing certain types of roads. Worse, people would have been incentivised to drive more and get their money's worth once they had paid the charge.

'I am on record as saying that I support road pricing – but not a crude scheme like this. My version would have abolished road tax and cut fuel duty.

'It would have seen those motorists opting to switch to lower carbon vehicles paying less, so if you were driving a clean car in a rural area for example, you would have been much better off than you are now.'