Though Greens support road pricing, they question whether the current government has the political will to introduce it quickly enough, and stress that any such system would have to be complemented by massive investment in public transport to provide people with alternatives.

Greens suspect road pricing would take years if not decades to come into force, and that until then better public transport and local congestion charging schemes offer a more speedy way of taking traffic off roads.

Mark Ballard MSP, Green speaker on transport, said, "Road pricing would reduce traffic and slash pollution, but the threat of climate change demands more immediate and effective measures - does Labour have the political will to put a system in place quickly or will they drag their heels?

"Labour did not fully back congestion charging in Edinburgh, and LibDems, SNP and the Tories, also opposed it.

“We suspect that the government wants to sound tough on this issue but will not take any meaningful action soon.

“Introducing congestion charging schemes and investing in high-quality affordable public transport can be done relatively quickly and have a real impact on pollution and traffic levels.

"Congestion costs the UK economy upwards of 20 billion every year so it's in everyone's interests that it is tackled. Road pricing is part of the solution but I doubt Labour or LibDems will treat this with the urgency it requires.

“In the long term, a personal carbon quotas scheme is the most fair and effective way of preventing pollution that wrecks the environment and seriously threatens public health."