A group of leading scientists has urged Prime Minister Rishi Sunak to call out figures in his party who they say are “dismissing the science” of air pollution.

In a letter to Mr Sunak, some 36 air pollution scientists warned there had been “mainstream political endorsement” of “suppression campaigns” aimed at denying the medical impacts of poor air quality.

Though Mayor Sadiq Khan’s plans to expand the Ultra low emission zone (Ulez) to cover the whole of Greater London is not referred to by name, it is understood to be the letter’s implicit focus.

Conservatives in City Hall and Westminster have argued against the zone’s expansion, saying that the £12.50 daily charge for non-compliant vehicles will hit people’s pockets in a cost of living crisis, while bringing “only a small change in air quality”.

But the letter’s chief author, Professor Frank Kelly of Imperial College London, said Mr Sunak should disassociate himself from “merchants of doubt” in the science behind air pollution – and tell his party colleagues to “not endorse them or emulate their pervasive claims”.

Professor Kelly told the Prime Minister: “Mainstream politicians have been attending rallies run by conspiracy theorists.

“They have been loudly repeating their dismissal of our science on social media accounts and broadcast interviews. They have spoken of not believing the science in the London Assembly and in Parliament.”

The scientists said their research has “uncovered the extent to which poor air quality contributes to the development of asthma, strokes, heart attacks, cancer and even dementia” – and that children and older people are especially vulnerable.

Professor Kelly added: “Not long ago we saw what happened when fossil fuel interests funded doubt on climate science. It cost us valuable time.

“We urge you to not let the same happen on the reality of the substantial impact that poor air quality has on our health.

“Instead, we ask you and your colleagues to value science and understand the incredible advantages it bestows upon modern society. We ask you to join us in making the case for urgent action on air pollution.”

Responding, Neil Garratt AM, leader of the City Hall Conservatives, said: “We have been clear in our commitment to reducing air pollution and tackling climate change.

“The authors of the letter ask us to disavow false claims and the individuals making them, but they do not tell us which individuals or claims.

“The Ulez expansion would produce only a small change in air quality according to the Mayor’s own independent analysis, which we must balance against the severe financial impact for those hit by the Mayor’s charge.

“It is irresponsible for anyone to conflate opposition to the Ulez expansion with science denial.”

The analysis referred to by Mr Garratt is an official assessment report on the impact of the expanded Ulez, carried out by the firm Jacobs.

It said that the “Proposed Scheme is modelled to result in a minor reduction (-1.3%) in the average exposure of the population of Greater London to NO2 [nitrogen dioxide] and negligible reductions (-0.1%) in average exposure to PM2.5 [particulate matter]”.

City Hall has previously responded to that point by saying it is “important to understand the impact of this [the expanded Ulez] policy in absolute terms”.

“For example, although NO2 concentration reductions are smaller in percentage terms than for the central London Ulez, in absolute terms there is a much larger volume of NOx emissions saved equating to 362 tonnes. This is in comparison to the 240 tonnes saving we saw in central London,” a City Hall spokesperson has said.

Professor Kelly in February said there were strong health grounds for expanding the Ulez.

He said: “We know that any delay in improving air quality is going to have an ongoing additional health impact on the citizens.

“That is why something like the Ulez, which is directly addressing the emissions which make our air quality poor, is something we really need as soon as possible.”