Transport for London (TfL) is reported to have misled the public about the benefits of the capital’s ultra-low emission zone (ULEZ).

It comes after a draft report leaked by The Sunday Telegraph showed an investigation was launched by watchdog the Advertising Standards Authority (ASA) earlier this year after hundreds of people complained TfL had exaggerated the extent to which the scheme had improved air quality.

The ASA draft report criticises “misleading” claims made about reducing levels of nitrogen dioxide (NO2) in TfL’s radio and newspaper advertisements.

Adding that recommendations state that two complaints about two radio adverts and one in a newspaper are to be upheld, according to the Telegraph.

Following the ASA’s investigation, it found two adverts were “misleading” because they “did not clarify” claims NO2 levels had “reduced by nearly half” as a result of ULEZ, and were based on “estimates or modelled scenarios” and not “actual figures”.

TfL 'misled public' in ULEZ health benefits, reports 

A second complaint, which is set to be upheld, found that an advert claimed deaths from pollution were higher in outer London had failed to make clear that the area had already been covered by ULEZ, the newspaper reported.

TfL spent millions of pounds on marketing ahead of expanding the ULEZ to cover the whole of the capital from August 29.

Mayor of London Sadiq Khan chairs TfL and it is understood the Mayor's office will strongly reject any suggestion the adverts were misleading.

Discussing the reports, a TfL spokesperson said: "We have received the draft recommendations from the Advertising Standards Authority (ASA) and are strongly challenging them.

“The ASA is not challenging the science. The science is absolutely clear about the significant 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.

“Scientific analysis based on modelled scenarios and estimates is standard practice in the scientific community.

“We are meeting with the ASA to take them through the data and explain in detail how it is used.

“It remains the case that the expansion of the ultra-low emission zone is playing a crucial role in the reduction of air pollution – improving air quality for everyone in London and reducing the harms to health associated with vehicle emissions.”

The ULEZ was expanded to reduce air pollution in the region, with vehicles entering the zone and not meeting requirements liable to pay a daily £12.50 fee.