One of the city’s worst ‘dirty air’ blackspots has been targeted by environmentalists in a campaign to persuade drivers to turn off their car engines when stationary.

Canterbury Green Party members were out in force in St Dunstan’s on Saturday morning where the level crossing causes traffic to back up.

Many drivers leave their engines running for up to five minutes while waiting for the barriers to lift which has resulted in the area recording some of the highest levels of pollution because of the exhaust fumes.

But Green Party campaigns manager Nathan Tough said the four hour action had resulted in benefits.

“Most of the drivers we spoke to were very aware and sympathetic to what we were trying to achieve and switched their engines off.

"In fact, as a result there was a tangible difference in the air quality which became less pungent as they day went on," he said.

Campaigners also handed around 250 leaflets which featured a photo of blackened filters from a mask worn by Green Party member Martin Baker over a two week period of cycling from Sturry to his work at the University of Creative Arts.

Mr Baker said: "I got a mask because I heard statistics about Canterbury’s air pollution being way above national guidelines but I never expected it to be this bad.

"What scares me is these filters only catch the larger particles, but apparently it’s the smaller particles that do the most damage."

Canterbury’s poor air quality has previously been highlighted by Professor Stephen Peckham, who is director of health policy at the University of Kent.

Average nitrogen dioxide levels are monitored by diffusion tubes at 27 points across the city.

Prof Peckham says nine of them show readings above the 40mg/m3 limit set by the EU and highlight pollution hotspots, including St Dunstan’s, Broad Street and Wincheap.

He estimates Canterbury’s pollution – caused largely by traffic congestion – is already claiming at least 100 lives per year.

Party county council candidate Henry Stanton said: "In light of Canterbury City Council running scared of a car-free day and with no plan in place for fixing Canterbury’s illegal air pollution, we are doing what we can to encourage drivers to make a difference to levels of pollution which is damaging health and claiming lives."

With 4,000 new homes coming, Canterbury is facing the prospect of more congestion, more air pollution, and more of our elderly dying prematurely.

He added: "Tests on children in polluted areas of London show that they have 8% less lung function than children raised in an unpolluted environment and parts of Canterbury are approaching similar levels of pollution. It is unacceptable that our council continues to be so complacent over this invisible killer."