Ahead of the treasury chief's forthcoming pre-budget report, the Sunday Times said the one-off point of purchase charge for high-polluting vehicles would be in addition to an increase in road tax prices.

Additionally, owners of more fuel-efficient cars would be eligible for a £2,000 rebate under the proposals.

The leaked proposals appear similar to the Conservative party's 'Quality Of Life' policy report, which recommends a new purchase tax on cars of up to 10 per cent depending on emissions. Those proposals were criticised by the government, with Treasury chief secretary Andy Burnham saying the Tories were raising green taxes to 'eyewatering' levels. The report is said to conclude that although the proposed changes strengthen 'the environmental signal', emission reductions would be limited. The paper also stated that motorists abandoning high polluting vehicles would lead to a loss of about £180m in fuel revenue within five years' time.

The proposals have been swiftly criticised by Sue Robinson, director of the National Franchised Dealers Association (NFDA), the body representing franchised car dealers. She said: “The motor sector has become the target of choice for political parties jostling to be the greenest during this year's conference season.” Robinson insisted the plan would have a limited environmental impact as it would only be fully levied on a small number of vehicles but would cause problems for dealers. “The impact on motor dealers could be considerable. Apart from increasing prices in the showroom, the need for a tax rebate on smaller vehicles could tie dealers up in a red tape knot,” said Robinson.