Greenpeace activists took to Kettering with a cutout of Mary Poppins wearing a pollution mask to voice their concerns over air quality.
Under EU rules, any single location in the UK is only allowed to breach hourly limits of 200 micrograms of NO2 per cubic metre of air 18 times in a year.
But Greenpeace says that this was breached in London just five days into the year.
Now activists are urging the Government to end the sale of new diesel cars, most of which pump out between two to 15 times the legal limits, and push manufacturers to rapidly shift to hybrid and electric vehicles.
Alan Heath, local Greenpeace activist, said: “It’s shocking that it’s taken only five days to break the UK’s annual limit of air pollution.
“Despite growing concerns about the health impacts of diesel fumes, the Government has done almost nothing to tackle car companies since they were caught cheating emissions tests.
“Unbelievably, the Government is still incentivising consumers to buy brand new diesel cars that are pumping out illegal levels of pollution.
“If cars coming off the production line had dodgy brakes, you know the Government would step in to sort it out.
“We urgently need to stop the sale of new diesel models until emission testing is truly fit for purpose.
“Better still, we need car companies to phase out diesel completely and concentrate on hybrid and electric alternatives. We need #cleanairnow.”