Mayor of London Ken Livingstone predicted this week that Gordon Brown will push ahead with a road pricing scheme as prime minister.
Mr Brown informally accepted the Labour leadership today. With a full manifesto not yet available, politicians and analysts have been speculating on possible policies.
Speaking at a C40 Climate Summit on congestion and climate change, attendees report Mr Livingstone said he expected Mr Brown to implement a national road pricing scheme during his leadership.
The shadow transport secretary Chris Grayling said he had heard "ever-increasing rumours" from the Treasury that Mr Brown sees road pricing as an important source of revenue.
"Road pricing could turn out to be the ultimate stealth tax," he wrote in an exclusive article for politics.co.uk
However, the secretary of state for transport Douglas Alexander insisted this week the government had no plans for a nation wide road pricing scheme until it had observed the effect of local small-scale schemes.
Writing for politics.co.uk, Mr Alexander said the government was working with local authorities to explore "targeted solutions" to specific transport problems.
He said: "Any local scheme will give us all a much clearer idea of how road pricing could work in practice.
"It's vital that everyone with an interest - private motorists, the business community, central and local government, road safety and environmental campaigners - is given the chance to see how schemes operate in the real world."
But, despite public scepticism towards road pricing, Mr Alexander repeated Tony Blair's warning that "doing nothing is not an option."
Liberal Democrat transport spokesman Alistair Carmichael has questioned the true extent of public opposition to a possible road pricing scheme.
He warned people not to allow the "myths" circulated by the Association of British Drivers to go unchallenged - pointing out the organisation also denies climate change is happening.
In an article for politics.co.uk, he said: "Whatever your views on road user pricing, for the good of our environment and our economy, the status quo is not an option.
"It is irresponsible not to look at new ways to price road use to ensure that those who pollute the most pay the most and to avoid gridlock on our roads."
But he echoed Mr Grayling's scepticism of Mr Brown. The chancellor "has only ever seen 'green taxes' as a way of increasing the take for the treasury," he said.
Mr Carmichael concluded "it is clear a national debate on road pricing is underway" and called on the incoming prime minister to make his position clear.