£25 charge will make pollution worse, says 'secret' study for TfL

Motoring groups have said the damage will be done by drivers of bigger vehicles threatened by the higher toll changing their routes to avoid central London, clocking up higher mileages in outlying areas.

Now research into the effects of the new charge, commissioned by Transport for London, whose chairman is Ken Livingstone, appears to support that.

The study was sent to the Mayor in January but has only now come to light. It emerged as carmaker Porsche demanded background documents in its legal fight against TfL's plans to implement the £25 daily charge for the highest polluting vehicles from October. The Mayor and TfL say the charge - for vehicles which emit more than 225g of carbon dioxide per kilometre - will reduce carbon dioxide overall. But the study, by the King's College enviromental research group, says in practice it will boost CO2 emissions in Greater London by 182,000 tonnes a year by 2012.

Researchers said the charge would create a "very high disbenefit" for CO2 levels and also for pollutants such as nitrogen oxides (NOx) and PM10 particulates - tiny particles that can cause heart and lung problems. The worst effects are forecast for outer London.

Andy Goss, managing director of Porsche Cars GB, said: "We always knew the environmental impact of this unfair tax would be minimal - now we know it will make matters worse.

"The Mayor and TfL need to explain why this report was not disclosed and why they want to increase taxes on motorists that will increase CO2. It seems absolutely clear that not only have Mr Livingstone and TfL not presented all the information to the public about the impact of his £25 charge, but they have also created a new tax on motorists that will do the exact opposite of its stated goal."

A separate TfL report to the Mayor has said the new charge will cut up to 5,000 tonnes of CO2 next year and 7,500 tonnes in central London in 2010.

But the King's study shows that, across Greater London, CO2 emissions would rise by nearly 184,000 tonnes by 2012, with just 2,200 tonnes saved in central London, giving a net increase of 182,000 tonnes. This is a rise of about 2.3 per cent compared with the current charging scheme.

Even the TfL report admits: "In the short term it is possible some cars liable for the higher charge may be moved outside central London. If this leads to a higher mileage then it could reduce the CO2 benefits."

Paul Watters of the AA said: "It's clear that with a daily charge of up to £25 many drivers will choose routes that circulate well away from the London charging zone rather than face a huge hike in motoring costs and dent in family budgets."

But today TfL said the methodology used by the King's researchers was "less robust and accurate" than its own, although both studies were considered by the Mayor in deciding to introduce the £25 charge.

A TfL spokesman added: "The potential increases in emissions of NOx and PM10 originally modelled are negligible in the short term.

"However, as we informed Porsche some weeks ago, even these figures have been very significantly overestimated. King's College... agree with this conclusion and are revising their report." He said TfL would " vigorously" defend itself against Porsche's legal challenge.