Tony Blair is to write to everyone who has signed the petition against road pricing in an attempt to dispel the “myths” about the proposed charging system.

Next week he will send all the signatories an e-mail defending the plan to hold regional trials of the pay-by-the-mile scheme.

More than 1.3 million people have now signed the petition on Downing Street’s website and the total could reach two million by next Tuesday, when the petition closes.

Ministers admit privately that the experiment in internet democracy has been a political disaster, but they hope to recover ground by taking advantage of having the e-mail addresses of everyone who signs the petition.

A government source said: “At least we can get directly in touch with those people who are so strongly opposed to road pricing that they signed the petition.

“They can expect a detailed reply in a day or two after the petition closes. It will address some of the myths circulated by those trying to ramp up support for the petition, such as the claim that the system will be used to catch people speeding and to track people’s movements.”

Douglas Alexander, the Transport Secretary, has promised that the technology will be used only to tackle congestion and not to determine the speed of a vehicle, even though it may have this capacity. He has also pledged that there would be safeguards to guarantee people’s privacy. Mr Blair’s e-mail is also expected to offer some reassurance about the revenues from road pricing, but will stop short of making a commitment not to raise the overall level of motoring taxes.

The Government has already said that it does not want to introduce a “tax on top of another tax”, implying that either fuel duty or road tax would be reduced to compensate for the introduction of road pricing.

The source said that Mr Blair and Gordon Brown, the Chancellor, agreed that the petition should not be allowed to undermine the Government’s policy of testing the potential benefits of road pricing in trials starting within five years.