A "yes" vote would need approval from the Scottish Executive, but could see the congestion charge in place by early 2006. Results of the ballot are expected around February 22.

London's mayor Ken Livingstone introduced the world's biggest congestion charge in February 2003, winning applause from environmentalists and brickbats from local businesses.

At five pounds per vehicle, the scheme has raised millions for public transport and cut congestion more than expected.

But it has drawn criticism from retailers who say their businesses have suffered.

Livingstone is backing Edinburgh's plans to introduce a similar charge, saying he battled through "doom and gloom" to bring in London's scheme.

Edinburgh Council estimates the charge, applicable to vehicles entering the centre of the city, would raise 760 million pounds over 20 years, a windfall it vows would be used solely to fund transport improvements.

But the plan is not without its critics.

Scottish Tory leader David McLetchie has described it as the "thin end of a wedge", warning it could lead to congestion charging across the whole of Scotland.

"In London we now see that Ken Livingstone is proposing to increase the congestion charge from five to eight pounds," he told the BBC.