Schoolchildren and parents staged a protest against the pollution around schools throughout Hampstead and Highgate which they claim is choking them to death.

Donning face masks, they called on London mayor Sadiq Khan to intervene to stop the Cycle Superhighway 11 (CS11) and the High Speed Rail 2 (HS2 schemes in their tracks.

They fear both planned projects will bring 475 extra cars and lorries per hour to the narrow streets around schools and pose a real threat to their health.

It comes days after the director general of the World Health Organization said air pollution is “one of the most pernicious threats” facing global public health and is on a much bigger scale than HIV or Ebola.

Dr Margaret Chan told the BBC Today programme that indoor and outdoor pollution was linked to the deaths of hundreds of thousands of children each year.

It also comes after Mr Khan called for cars to be banned from roads near schools in order to reduce air pollution.

The Mayor of London accused the government of “ignoring” toxic air and criticised chancellor Philip Hammond for not raising taxes for the most polluting vehicles in last Wednesday’s budget.

Mr Khan said: “Forty or 50 years ago we thought smoking was bad and yet our forebears took no action.

“Now, we know air quality is a killer, it makes you sick and no action has been taken. It’s a health emergency.”

Solicitor Jessica Learmond-Criqui, who coordinated the protest with Hampstead mums and pupils outside St Stephen’s, in Rosslyn Hill, said: “Hampstead is already bad and in excess of safe NO2 levels for adults and kids. The readings are off the scale.

“Hampstead and Belsize area is the biggest educational park in the world. There are over 55 schools and colleges in Hampstead and Belsize with at least 12,500 school children going to school here every day – many under seven years old,” she said. “Why is the mayor encouraging TfL to force up to 475 extra cars per hour into some of our narrowest residential side roads?”

She also believes that work on a new immunology unit in the grounds of The Royal Free Hospital will cause more pollution with 80 lorry movements per day.

“The path of those lorries is right at the bottom of the garden of Hampstead Hill school.

“What about the kids in that school breathing in the lorry fumes? Why does the mayor’s rhetoric not apply to those kids and why is the Royal Free being allowed to get away with gassing these children in this way?

“Mayor Khan’s rhetoric does not live up to the reality of the outcome of some of the policies which he supports,” she added.

Ms Learmond-Criqui said: “While we support cycling, CS11 in its current form is not right for our area.

“I would invite the mayor to reach out to community leaders and give them the support they need to come up with a safe scheme for cyclists but which won’t increase the toxicity on the young and old lungs in our area,” she said.