By midnight tonight, around 1.7m people will have played their part in one of the most popular and unexpected experiments in online democracy the UK has had.

For the past three months, from Land's End to Shetland, men and women have been putting their names and e-mail addresses to a petition on the Downing Street website calling for ministers to scrap all plans for road pricing.

Tracking and billing every vehicle in the country by satellite is not only "sinister and wrong", the new pay-by-the-mile tax will be unfair on those living apart from loved ones and the poor, runs the petition's rallying cry.

The threat of paying extra for the school run or a weekend drive has generated a huge response from the public, catching the government off-guard and prompting Tony Blair to promise a reply to all who sign the petition before it closes tonight.

But with the technology to pinpoint every vehicle on the road still a decade away and politicians scared of enraging the 74% of households regularly using a car, is the reaction proportionate?

The Westminster government has certainly put itself behind road pricing in theory, suggesting new charges could be offset by cutting fuel duty and road tax, and improving public transport to offer drivers an alternative.

The busiest roads would be the most expensive to drive on - estimates go up to £1.50 a mile - while quiet roads, such as those in rural areas, would be priced at the lowest level or not at all.

Last December, the idea seemed sealed when a Treasury report - for which read approved by Gordon Brown - warned congestion would cost the economy £22bn a year by 2025, the equivalent of £900 a household. Stephen Ladyman, UK roads minister, also declared recently that a national roads pricing scheme was "inevitable". However, 1.7 million angry voters are hard to ignore, and "inevitable" covers an awfully long time.

According to Paul Watters, head of roads and transport policy with the AA, a more likely short-term future is a series of local congestion schemes on the lines of the one pioneered in London by Mayor Ken Livingstone in 2003. Mr Watters said that over the next 10 to 15 years he expected Manchester to follow suit, and speculated Glasgow might dabble with the idea, despite the massive rejection of a congestion charge in Edinburgh.

"I think the government do understand motorists' sensitivities. The sad thing about what the government is doing is that it keeps telling us road pricing is worth thinking about, yet don't tell us how it's going to work in practice. People should be sceptical but not paranoid about it."

The difficulties certainly should not be underestimated. Vast, complicated and intrusive, any satellite tracking system would also need to be backed up by a massive billing system.

At the moment, the government cannot guarantee cars on the road are even taxed and insured. Why should rogue drivers be any keener to install a black box to monitor their every move, and pay up to £600 for the privilege?

Moreover, despite some talk of road pricing being piloted, it would need to arrive as a big bang''. It would be impossible to cut fuel duty in some parts of the country but not others without causing yet more congestion as people flocked to trial areas to fill their tanks cheaply.

Although tracking technology could be tested to generate notional bills, they would not change driver behaviour, making it difficult to say if a nationwide rollout would work.

In Scotland, where car ownership is lower than the rest of the UK, congestion policy is lagging behind Westminster. In part, this is because the UK government funds work on schemes south of the border. So far, 10 areas have been given money to develop congestion schemes, including Manchester and Bristol.

In Scotland, councils have also been chastened by the backlash to the early Edinburgh proposal.

Duncan McLaren, chief executive of Friends of the Earth Scotland, yesterday urged MSPs to look hard at congestion charging as an alternative to more road building.

However, when our politicians debate the issue at Holyrood on Thursday, they are more likely to be looking hard at their shoes as they avoid saying anything too contentious before the election.

A Scottish Labour spokesman last night said road pricing had "not been ruled outand doing nothing was not an option", but was not ready to name his party's particular prescription.

Fergus Ewing, SNP transport spokesman, said road pricing was "plainly a possible system", but not one which energised him. The Tories are fiercely opposed to any form of road charges.

The executive is pro-road pricing in theory, so long as it is part of a UK-wide scheme - as are the Scottish LibDems, although if UK reform remains "glacial" they would lobby for road and fuel tax to be devolved in order to scrap them and go it alone on pricing.

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