Green campaigners yesterday accused the Scottish Government of reneging on its pre-election promises to reduce carbon emissions and tackle climate change.

They said moves to abolish tolls on the Forth and Tay bridges were a "lose-lose situation" because it would increase road congestion and leave less money to be spent on improving public transport.

In its election manifesto, the SNP vowed to reduce carbon emissions by 3% year-on-year, culminating in an 80% cut by 2050.

But, giving evidence yesterday to the Holyrood committee that is examining the government's Abolition of Bridge Tolls Bill, environmentalists said that aim was being placed in jeopardy just four months after the party took power.

John Lauder, the director of Sustrans Scotland, which campaigns for sustainable transport policies, said: "This does absolutely nothing to put down a marker to say the Scottish Government is going to take carbon emissions seriously."

Richard Dixon, director of WWF Scotland, said scrapping the tolls was a "double whammy" for the environment.

"We have proposals to take away tolls, which will encourage people to use cars and not public transport," he said. "At the same time, that takes away a revenue stream we could be using to fund the alternatives."

Mr Dixon also pointed out that an independent study into the impact of removing the tolls had predicted it would lead to an extra 9000 tonnes of carbon dioxide being released into the atmosphere.

He added: "This is a key challenge for the SNP administration. It has made very good promises on climate change, but this is clearly an area where it is going to have difficulty reconciling it with the reality of running Scotland.

"This bill takes us in the wrong direction and sends a very clear signal to the public that they are being encouraged to use the car in favour of public transport."

The Transport, Infrastructure and Climate Change Committee also heard from the authors of the toll impact study, John Stephens and Steve Hunter of consultants Steer Davies Gleave.

Mr Stephens said removing the tolls did not represent value for money for road users.

He said: "The costs of increased congestion outweigh the benefits of not having to pay the bridge tolls."

Officials from Dundee, Fife and the City of Edinburgh Councils also admitted they have not been consulted by the government over the scrapping of the tolls.

However, the Dundee and Fife representatives said they were in favour of the move.

A spokesman for the government said: "We believe it is an injustice for the communities of Fife, Tayside and the Lothians that tolls remain on the Forth and Tay bridges, while elsewhere in Scotland they have been removed."