The adverts, which were broadcast and published between January and June, claimed that the existing Ulez in central London had “almost halved levels of nitrogen dioxide (NO2)” and that “most air pollution related deaths actually occur in outer London”.
But a draft of the watchdog’s conclusions, leaked to The Sunday Telegraph, found that the Ulez adverts were misleading because they “did not clarify” that claims about NO2 levels were based on estimates or modelled scenarios and not actual figures.
The investigators said: “In the absence of qualifying information consumers were likely to understand that the claims were based on actual figures, not estimates or modelled scenarios, and that NO2 concentrations had been seen to reduce by almost a half.”
The report was leaked after being sent to interested parties before any potential amendments, ratication and publication.
It is believed TfL will “strongly challenge” the draft conclusions.
A TfL spokesman said: “The science is absolutely clear about the signicant harm of air pollution on people’s health and that estimated premature deaths from air pollution are higher in outer London than in inner London. We are confident that the advertisement is accurate.”
The advertising watchdog refused to comment on the leaked document but a source told the Sunday Telegraph that the final ruling had not been issued and so the fiundings could change.
The final ruling is set to be officially released in the next few weeks.
A total of 578 people contacted the ASA, claiming TfL had exaggerated the extent to which the zone would improve air quality.