Schools in a borough rated among the worst in the country for air pollution are campaigning to stop drivers leaving their engines running while dropping off and collecting children.

Banners have been put up outside Dartford Primary Academy as part of a borough council initiative to keep children safe from dirty air, with three more schools due to do the same.

The air in the borough is said to be at levels equivalent to smoking 144 cigarettes a year.

An air quality study which looked at each individual square kilometre of the country found one part of the town – alongside the A282 Dartford Tunnel approach road to the north of Bean – had the worst levels of pollution in the UK.

The survey found 23 micrograms of pollutants per cubic metre of air, which is more than double the World Health Organisation's (WHO) recommended guideline of just 10.

Earlier this year, Dartford missed out on government funding to deliver projects to help reduce the impact of pollution on people's health after deciding not to apply.

At the time, council leader Cllr Jeremy Kite (Con) said: "The business of tackling air quality is not about single episodes of activity. It is about a long-term plan.

"Dartford has got some very specific issues. When you look at the grants and what they have been used for, very few of those would have tackled our core problem which relates to the strategic network."

Dartford council hopes its new project will educate drivers on air pollution.

Banners appealing for motorists to switch off their engines while waiting outside schools have been put at the main entrance of Dartford Primary Academy in York Road, where there are lots of offending cars.

Cllr Kite said: "It is unavoidable that some parents and carers will have to drive their children to school. But what they can avoid is pumping potentially harmful pollutants outside the school gates.

"We pride ourselves on keeping Dartford’s air clean, despite the challenge caused by traffic on the M25 and A282.

"Encouraging people to switch off their engines whenever possible is a simple way of reducing air pollution. It is the council’s hope that this message will spread beyond the playground and bring about a positive behavioural change."

Schools are daily hotspots for "idling", which is when a vehicle remains stationary unnecessarily for at least a minute. This means children face greater exposure to harmful pollutants than many others just by being picked up and dropped off.

Despite the improvements made in air quality over the years, air pollution is still recognised as a risk to health.

Exposure to air pollution has health effects at every stage of life, from before birth into old age. The damage is sometimes gradual, and may not be apparent for many years.

The anti-idling project is just one of many measures included in the 2022 Air Quality Action Plan and has been produced as part of Dartford's statutory duties required by the Local Air Quality Management framework.

It outlines the action the council will take to improve air quality between 2022 and 2027.