The row between Porsche and Ken Livingstone over the London Mayor's plans to impose a £25 congestion charge on the most polluting vehicles took a fresh twist yesterday after the car manufacturer released a report claiming the move would inadvertently result in an increase in carbon emissions.

The report, which was discovered by Porsche, was undertaken by researchers at King's College London for Transport for London (TfL) and claimed that the increased charge would increase carbon emissions across greater London by 182,000 tonnes. It argued that any savings within central London would be negated by an increase in the number of car journey emissions outside the congestion zone.

The findings mirror a similar Land Rover-sponsored study from the Centre for Economics and Business Research, which claimed the changes would have a negligible impact on emissions as owners of the most polluting vehicles would be likely to simply pay the charge or perhaps even buy a second smaller car that they would then only use in the congestion zone.

Porsche, which has launched a judicial review against the changes to the scheme, claimed that King's findings contradicted claims from the mayor and TfL that the move would deliver significant environmental benefits.

However, TfL rejected Porsche's claims CO2 emissions would rise and accused the company of attempting to deflect attention from its cars' high emission levels.

TfL said that the King's College research had focused on emissions of Nitrogen Oxides (NOx) and Particulate Matter (PM10) and that while it projected a negligible short-term increase in these emissions the figures were now being revisited.

Sean Beevers, the academic in charge of the air quality modelling work at King's Environmental Research Group College, admitted there had been a problem with the initial research based on "ambiguity in the assumptions" underpinning the research.

"As a consequence of this process, moving forward we are currently providing TfL with revised assessments," he said. "These are likely to show that the PM10 and NOx effects are smaller than previously projected and that our estimates of the CO2 effects are broadly comparable with those that have been produced by TfL."

Malcolm Murray-Clark, managing director planning at TfL, insisted that the agency's own analysis of the impact of the new charge on CO2 levels showing that emissions from cars travelling to and from the zone will fall by 5,000 tonnes by 2009 remained "accurate and robust".

"We have made clear we will vigorously contest Porsche's claims and any tactics designed to deflect attention away from the main issue," he added. " They should focus their attention on cutting CO2 emissions from the cars they produce, rather than pursuing this pointless legal action."