It was revealed last month by the Telegraph that Shirley Rodrigues - London’s deputy mayor for the environment - contacted academics on three occasions, after studies and articles were published questioning the benefits of the low emission zone (Lez) and ultra low emission zone (Ulez).
The mayor’s office said Ms Rodrigues has “helped to lead the work on cleaning up London’s toxic air”.
City Hall maintains that Mr Khan’s decision to expand the Ulez across Greater London will bring significant improvements to air quality. The organisation says that the Ulez is projected to reduce by nearly 10 per cent nitrogen dioxide emissions from cars in outer London and cut exhaust emissions of particulate matter from cars in outer London by nearly 16 per cent by the end of 2023.
According to reports, Ms Rodrigues in 2018 asked if Professor Chris Griffiths, of Queen Mary University of London, could “reword” a Lancet study’s conclusion that found “no evidence” of health benefits from the Lez to children’s lungs.
Ms Rodrigues said in an email to the scientist: “It reads like Lez or similar have no impact at all.”
Prof Griffiths refused the request, replying: “Apologies - it’s difficult to alter the sentence you refer to as it’s what we set out to look for but didn’t find.”
In 2021 and earlier this year, Ms Rodrigues wrote to Imperial College London’s Professor Frank Kelly - a world expert on air pollution whose team has previously received funding from Mr Khan’s office - on both occasions asking him to counter negative research and reporting about the Ulez.
The deputy mayor emailed Professor Kelly to ask whether he would be willing to “set the record straight”.
Her initial email was sent after a separate group of Imperial academics had published a study suggesting the central London Ulez had had a relatively small effect on air pollution at its launch.
Ms Rodrigues went on to work with him to draft a press statement to send out in his name.
Tory AM Peter Fortune, said in August that it was “unacceptable” that Mr Khan and his deputy “conspired to silence legitimate research because it would damage the mayor’s reputation and credibility”.
He added: “The mayor’s office certainly shouldn’t be dictating emails for press releases or squashing dissent.”
Speaking at an Assembly meeting on Thursday - the first since the Telegraph’s articles were published - Lib Dem AM Caroline Pidgeon said: "We called for an investigation at City Hall into what has or has not happened, in order that we could have more facts - because I think Londoners need to know the facts on this…
"Any report of politicians applying political pressure to change the outcome of a scientific report should worry anyone, in a democratic society. It almost feels like something Donald Trump might do in the States.”
She added: "Political interference in academia work would risk undermining the public's trust, not only in politics, politicians, but also in science and scientific studies.
“We think, if political interference has taken place by officers or members of the Greater London Authority, it's a serious risk to the reputation of our organisation as a whole."
Tory AM Emma Best agreed, saying, "I certainly think it's important that that happens [an investigation], and we recognise how wrong this has been".
Ms Best went further at an earlier point in the meeting, telling the chamber: "This is such an abdication of duty, and actually I think this entire Assembly should be calling on the deputy mayor to resign from her position.
“I genuinely mean that, because those emails and that exchange is not OK."
A spokeswoman for the Mayor of London said: “The deputy mayor has helped to lead the work on cleaning up London’s toxic air - acting upon the expertise and advice of London’s world-leading scientists.
“It is standard practice across government to commission independent experts to carry out research to inform the work we do.”
The calls for an investigation came as Ms Best unsuccesfully attempted to pass a formal motion in the Assembly which called on Mr Khan “to scrap the expanded Ulez in light of these revelations and the damaged credibility of the Mayor’s claims about the impact of the expansion on air quality”.
The motion failed to gain majority support, with only the Conservative group voting in favour.
Labour AM Leonie Cooper said: “No level of air pollution is safe. It’s quite clear that the World Health Organisation has said that, and expanding Ulez will assist with improving air quality for an extra five million Londoners.”
She added: “To ask the mayor to go back on Ulez, and scrap it, on the basis of an academic disagreement from five years ago, this is going back to 2018, is a foolish idea and must be resisted.”