A climber, campaigner and dad who has quite literally been shouting about Brent’s dirty air from the mountaintops is urging motorists to switch off their engines at traffic lights and while stuck in queues.

Some 17,000 children in Brent are being exposed to illegal levels of air pollution, according to data published by the London Atmospheric Emissions Inventory. So for the last two years, David O'Brien has carried his son's notes and messages about the problem to the top of Everest to make a symbolic - but important - point.

Young Flynn O'Brien attends Ark Franklin Academy which sits on the edge of the highly polluted Chamberlayne Road. As reported in the Kilburn Times in May 2018, Ark Franklin Academy and John Keeble School in Crownhill Road, Harlesden, were the two worst polluted schools out of 50 in the mayor of London's air quality report.

Chamberlayne Road was not among the "Low Emission Bus Zones" announced by Sadiq Khan in 2017, which included Kilburn High Road. Only low-emission buses are allowed to run in these areas, either through the rollout of new fleets or through retrofitting existing vehicles.

Flynn's note in 2017, addressed to Sadiq Khan and taken to the top of Mount Everest, said: "My dad climbs Everest and can breathe clean air. I go to school and breathe polluted air."

Last year his poster read: "Dear Mr Mayor, can you please ask drivers to turn off their engines when stuck in traffic outside my school?"

The council began giving motorists on-the-spot fines in March if they were caught parked with their engines running for more than a minute and didn't switch them off when asked by a pollution officer.

Expedition leader David, who lives in Berens Road, Kensal Green, said he didn't believe motorists should be fined, but felt could do more.

The 53-year-old dad-of-two said: "Whilst [my son's] poster relates to his school, this is really a message that relates to all schools across London because a lot are affected by pollution.

"There are two solutions. One of them is to make Chamberlayne Road a Low Emission Bus Zone. I don't know why they didn't include it, I've written lots of emails to TfL.

"And the other is for motorists to turn their engines off at traffic lights and in traffic jams right across London.

That would make a huge difference to our air quality. It's not to fine people, not say you have to do it, but to encourage people. A marketing campaign wouldn't cost a lot."

He added: "The worst place to be in a traffic jam is not walking along next to it, it's sitting in your car, and I don't think enough people know that.

"If you're in a queue of traffic you really want the person in front to switch their engine off because unless your filters are doing a great job they're not going to be sucking out the pollutants, and you're going to be breathing them all in."

A TfL spokesperson said from next October all of London would be a low-emission bus zone. All new single-deck buses will be zero-emission, with the entire fleet eventually becoming emissions-free - but not until 2037.

Meanwhile Navin Shah, Brent and Harrow's Assembly Member, has urged parents and pupils to take part in what remains of October's International Walk to School Month.

Mr Shah said: "Whether it's in the playground or in the classroom, we want our children to be safe, healthy and protected from toxic air.

"It's not easy for parents balancing family, work and all their other responsibilities. We know it's not always possible, but if they can sometimes leave the car behind they'd be making a significant contribution to reducing air pollution. If they do need to take the car, making sure they don't leave the engine idling will also help in reducing toxic air."

A study commissioned by Mr Khan last year found air pollution levels were worse inside classrooms than outside. Public Health England has since called for an end to engine idling and congestion outside schools.

Transport for London (TfL) is rolling out an accreditation scheme for schools - "STARS", or "Sustainable Travel, Active, Responsible, Safe" - to promote the uptake of "active travel" such as walking and cycling to replace car journeys.

"As Londoners," added Mr Shah, "we all have a part to play in cleaning up our air and our environment.

"This will help us to address existing health inequalities and will benefit the next generation."