The Government will never persuade the public to accept road pricing unless it is more honest about how the revenue will be used, the AA has said.

The motoring group said that ministers could lose the argument before even the first trial of the system, under which drivers would pay by the mile on congested roads. A petition against the scheme on the Downing Street website has embarrassed the Government by attracting about 1.2 million signatures. At times yesterday would-be petitioners had difficulty in gaining access to the site, such was the response from drivers.

The AA urged the Government to tell motorists whether the tolls would be in addition to, or instead of, existing taxes and demanded clarity on whether any additional revenue would be used for improving the transport network. Paul Watters, the AA’s head of transport policy, said: “People only see extra cost on the horizon, rather than a readjustment in how they pay. Transparency and stating guiding principles would help to give the public a better understanding. Those principles should include a commitment to reducing other motoring taxes and ring-fencing revenues.”

Douglas Alexander, the Transport Secretary, said that an e-mail encouraging signatures to the online petition contained several “myths”. The campaigners oppose increases in road taxes and the installation of tracking devices in cars.

Mr Alexander, who has denied that the system would be used to catch speeding drivers and has promised that privacy would not be invaded — countering two of the “myths”, played down the significance of the campaign, as “just one contribution to the debate”. He said that he expected similar-sized petitions in favour of the scheme. Officials said later that they were not aware that any had been organised. No decision has been taken on a national scheme but the Government is developing trial schemes in ten areas.

A Department for Transport official said: “Doing nothing is not an option. We welcome all debate, but it must be based on fact and not fallacy. The first step to achieving this is to demonstrate through local pilot schemes how road pricing can tackle local congestion.”

Mr Alexander told the BBC: “We have got a big response to this petition. I imagine there will be other petitions in the future with large responses, but it is an important part of the debate that we want to see.” Speaking on the Radio 4Today programme, he said: “A number of myths have been perpetrated and that is why I welcome the opportunity to set some of the facts straight.”

Paul Biggs, of the Association of British Drivers, told GMTV: “The only way road pricing can work is to price people off the roads. That is one reason they will sign the petition. Another reason they will sign it is that they are going to be traced wherever they drive.”

The department said: “Public acceptability of such schemes is one of the milestones that has to be achieved. We have always said that we have to see the results of the pilot schemes before we make a decision.”