Legal air pollution limits for the whole year have been broken just five days into 2017 in London, figures show.
Brixton Road, Lambeth has claimed the "dubious honour" of being the first air quality monitoring site to see levels of pollutant nitrogen dioxide exceed the annual hourly limits less than a week into the new year.
European Union limits demand that maximum hourly concentrations of nitrogen dioxide, which is mostly caused by road traffic in towns and cities, are not exceeded for more than 18 hours a year.
But monitoring by the London Air project from King's College, London, showed that the rules had been breached by 9pm on Thursday for the pollutant, which is linked to heart and lung problems and even early deaths.
The news, which saw a London street break the rules even earlier than last year when Putney High Street exceeded the annual 18-hour limit for nitrogen dioxide by January 8, prompted an angry reaction from clean air campaigners.
Other London roads are expected to exceed the limits shortly.
Dr Penny Woods, chief executive of the British Lung Foundation, said: "It's shocking that pollution limits in London have already been breached for 2017 - this shows the extent of the public health crisis we are facing.
"The mix of these toxic air pollution levels with freezing temperatures poses a serious risk to people with lung conditions and can affect all of our health."
Environmental law firm ClientEarth, which has repeatedly taken the Government to court over its failure to act on air pollution, called on London Mayor Sadiq Khan to deliver on his promises to tackle the problem and for national action from ministers.
ClientEarth lawyer and Brixton resident Alan Andrews said the breaches were "another shameful reminder of the severity of London's air pollution".
Mr Khan has promised a bigger ultra-low emission zone in 2019, and to deploy the cleanest buses on the most polluted roads, Mr Andrews said, but warned that Londoners could not wait three years and immediate action was needed.
And he said: "While London has the worst air pollution, this is a national problem which requires a national solution.
"The Government's draft plans to tackle air pollution, as ordered by the High Court, are due in April. They must include a national network of clean air zones, which stop the dirtiest diesel vehicles entering pollution hotspots.
"They also have to stop the perverse fiscal incentives which encourage people to use diesel vehicles and instead help them to buy cleaner ones."
Friends of the Earth called for plans to phase out diesel vehicles as part of a 21st century Clean Air Act, deliver stronger clean air zones across the country, expand London's ultra-low emissions zone, curb road-building and invest more in cycling and public transport.
FoE campaigner Jenny Bates said: "Air pollution is a major health threat, particularly to children and other vulnerable people, contributing to around 40,000 early deaths across the UK every year.
"Road traffic is the biggest culprit - and diesel is the worst. This is why the Government must take much bolder and quicker action including planning to phase out diesel by 2025."
Greenpeace campaigners staged a protest against the problem, with children's champion Mary Poppins soaring over Parliament in a pollution mask calling on politicians to clean up the UK's air to protect children's lungs.
They want the Government to end the sale of new diesel cars, in the wake of the Volkswagen emissions scandal, and push manufacturers to rapidly shift to hybrid and electric vehicles.
In September 2015 it emerged that Volkswagen had fitted software to around 11 million of its diesel cars worldwide which caused them to release fewer smog-causing pollutants during tests than in real-world driving conditions.
Paul Morozzo, clean air campaigner at Greenpeace, said: "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."