John Vidal is environment editor at the Guardian. He has reported from over 100 countries, breathed some of the cleanest and most polluted air on the planet, and wrote McLibel, Burger Culture on Trial.

Air pollution is as old as London. And the public are becoming concerned about it again. Will we ever be able to breathe safely in the capital?

Something changed in London in April 2014. People woke to warnings that the air was full of dust from the Sahara desert. Cars were orange. Windows were dirty. David Cameron abandoned his morning jog but dismissed the cause as a ‘naturally occurring weather phenomenon’. Emergency services were hit by a surge in 999 calls, complaints about breathing problems rocketed and people were urged to avoid strenuous outdoor activity as the dust enveloped the city.

Cameron was partly correct. The dust had indeed been swept 1500 miles north from Africa, but he and other politicians missed the fact that it coincided with a chemical smog – caused largely by London’s traffic fumes – which, for once, the Sahara dust made visible.

The timing was also significant. Just a few weeks before, nearly all the main roads in London had been found to have illegal levels of pollution. The air in the capital had just been declared the worst in Britain and children living near busy roads in east London had been found to have stunted lung growth. It did not matter that the Sahara dust episode was a rare occurrence: for most Londoners, April 2014 was the first time in many years that they became aware that the air they were breathing was foul.

Since then, London’s air has barely been out of the headlines. Ten days after the dust, Public Health England declared that 1 in 12 of all deaths in Kensington and Chelsea, and slightly fewer in other boroughs, were linked to air pollution. In quick succession, Oxford Street was then found to have some of the worst nitrous oxide levels in the world, largely emitted by buses and taxis; Boris Johnson proposed an ultra low emission zone for the centre of London to start in 2020; the government was told to come up with a new action plan for pollution by the Supreme Court; and, in July 2015, researchers at King’s College London declared that 9500 Londoners a year were dying from polluted air, more than doubling previous estimates.

The King’s College study for the Mayor of London was one of the last pieces in a scientific jigsaw. Previously, deaths from long-term air pollution had been counted only against the quantity of PM10s – minute particles, including unburned carbon emitted by all engines – in the air. For the first time, the King’s researchers included an estimate of the number of deaths from NO2 gas, largely emitted by diesel engines. To top it all, in October 2015 VW was caught illegally cheating air pollution laboratory tests on many of its diesel cars.

All this increased attention on London’s air has surprised and worried the public and policymakers. For some years, the authorities had been able to downplay air pollution. Environment groups had wanted to talk more about climate change. Other issues – Heathrow, river crossings, congestion and parking – had crowded out air quality.

From being something that most people took for granted as unpleasant but bearable, London air is now being talked of openly as dangerous, an assault on a basic right to breathe clean air, its threat made more sinister by the fact it is largely invisible and unavoidable. We all know now that the city that likes to bill itself as the most international and most economically successful in the world is heavily polluted, and is paying a heavy price.

From stench to the big smoke

Concern about London air is nothing new. In 1285, King Henry 111 was so revolted by the stench of burning coal combined with the whiff of London’s slaughterhouses and latrines that, like other rulers before and since, he set up a commission to investigate the quality of the air. When it reported 20 years later, he banned the burning of coal, ruling that offenders would face “grievous ransoms”.  His law was widely ignored.

History shows that London’s air has changed its chemical composition many times. In the 14th century, home counties forests were felled for firewood, wood prices in the city soared and industry turned to charcoal. In the 18th century, as coal became cheap, the middle classes moved west to avoid the foul air emanating from London’s factories.

For the subsequent 200 years, the burning of coal defined what Londoners saw, breathed and smelt. Soot blackened 18th-century buildings and clothes, filled the air and cut short lives. Nineteenth-century visitors to the capital remarked that they could see and taste the pollution, smell the sulphur and spit out the specks of dust that drifted over London in great sound-deadening clouds that absorbed the light and turned everything a surreal sepia colour.

John Evelyn, the diarist, gardener and contemporary of Samuel Pepys, wrote the first and greatest essay on London’s air. He sent his treatise, Fumifumigum, to King Charles in 1661, proposing that all polluting trades be banished from the city and that people should burn wood rather than sea coal. Just as the Chinese authorities, until very recently, viewed air pollution as a sign of healthy industrial and national progress, neither Charles nor London was ready to address the problem.

Scientific ignorance continued to prevail: 18th-century chemists and physicians, backed by industrialists, claimed that the smoke from 100,000 London hearths and factory chimneys was benign and could actually protect people against the ‘miasma’ of rotting vegetation that was said to be the cause of the city’s fumes, fogs and bad odours. When plague struck London in the 16th and 17th centuries, city officials urged residents to build coal bonfires to disinfect the air.

By the early 19th century, vast quantities of coal were being transported to London from across Britain. In winter, when the air was cold and still, dense fogs developed, but these were blamed on rural areas. Fog, or ‘smog’ as it was later called, was thought to be incapable of forming in cities, and the very conditions that made it likely – cool temperatures and still air – increased the amount of coal that people burned to keep warm, preventing the smoke from dispersing.

Modern science did not catch up with London’s air pollution until the late 19th century. In 1850, TB sufferers were still being pressed to inhale coal smoke. Robert Angus Smith, the chemist who coined the term ‘acid rain’, said in 1859 that smoke acted as a disinfectant and asserted that the high sulphur content in British coal made London smell sweeter than its continental counterparts. Twenty years later, the Lord Mayor of London could suggest that smoke abatement might actually harm public health and claim that malaria had been swept from the city when the great factory chimneys of east London were erected.

As public health science progressed, however, Victorian social reformers rose against the prevailing, utilitarian view that pollution was primarily an economic concern. London became known as the ‘big smoke’ and its notorious fogs became linked in the public and official mind to coal smoke.

Chief among the reformers were Octavia Hill and Ernest Hart, better known for founding the National Trust. Setting up the Fog and Smoke Committee in 1880, the well-connected pair convinced the Lord Mayor to give them offices in the Mansion House to lead the charge on London’s air pollution. Soon, The Lancet, the voice of the medical profession, declared that London’s air had become ‘a grave national calamity’. Even the industry periodical Chemical News urged ‘sanitary reform’ and the meteorologist reformer William Napier Shaw described London’s air pollution as ‘aerial sewage’.

Even though Hill, Hart and other reformers avoided questioning Victorian faith in progress and adopted a conciliatory approach to industry, they were dismissed by industrialists as ‘dilettantes’, ‘agitators’, ‘ridiculous’ and ‘unscientific’. Yet they convinced the public that change was needed. With other clean air societies in Manchester and the north, they pressed for legal and cultural change and by 1900 they had won both the scientific and moral arguments. Bit by bit, cities, MPs and the public got the message that progress could not come at the expense of health. Industry resisted change but the end of coal in London was in sight.

Even so, it took two great wars and a massive ‘pea souper’ smog in London in 1955, which killed around 2300 people, before government finally adopted the Clean Air Act, banning coal burning in the city once and for all, as King Henry had proposed 600 years earlier. This time there was barely any dissent in parliament.

But it was almost an anti-climax. By then there was a new threat. In a few decades, the automobile fundamentally changed the composition of London’s air yet again.

The worst air in Britain

As cars and lorries began to flood London’s postwar streets, new, more insidious gases and chemicals filled the air. Coal dust could be seen and spat out; sulphur could be prevented getting in to the mouth with a handkerchief filter. But petrol and diesel fumes were practically invisible and odourless. Instead of particulates big enough to see and cough up before they reached the lungs, unburned carbon from the internal combustion engine could reach deep into the bloodstream with no immediately apparent effects.

For a while, though, London councils more or less convinced themselves that air pollution had been cured and that the occasional smog, including pollution that had drifted in from the continent or the countryside, was acceptable.

Starting in the 1990s, a new generation of scientists and activists began to warn that the toxic soup of nitrogen oxide gases and minute particles of unburned carbon and chemicals released in the London air might be just as dangerous to health as coal dust and smoke. Along with respiratory and lung diseases, the new air pollution was linked to cancers, dementia, heart diseases, asthma and other illnesses.

Today we know that the worst air in Britain is not found in the old industrial heartlands of Glasgow, Newcastle or Birmingham, but on the busiest and most congested streets of London. And instead of pollution being concentrated in the places where the poor live and work, it is just as likely to be bad in rich boroughs like Kensington and Chelsea as in the poorer patches of town.

The scale of the political problem facing London is now recognised to be massive. Technical fixes, like spraying roads with glue to collect pollution, have been tried but there is growing acceptance that the only way air pollution can be reduced sufficiently to meet the legal limits is by banning the dirtiest vehicles, or even making much of central London car-free.

Meanwhile, plans for massive new developments like bridges, tunnels, airport expansions and retail developments are in jeopardy – because if they increase traffic they will increase pollution and are therefore open to court action.

Just as the 19th-century social reformers won the moral and scientific arguments and forced London to clean the air of coal, so a new generation of scientists, envi­ronmental activists and community leaders is driving Transport for London and the Mayor to rethink the place of the car in the city. They have science, the law and public opinion on their side and their tails are up.

Octavia Hill and others knew they wanted an end to coal burning, and the new reformers, with a vision of London as a pleasanter, more attractive and healthier city, are also demanding specific actions. Backed by the Supreme Court, which has demanded that London improves its pollution rapidly, and by Europe, which is threatening ‘grievous ransoms’ just like King Henry, the city is being dragged into the 21st century.

Today, the demands are city-wide pay-as-you-go driving, a much bigger Ultra Low Emission Zone (ULEZ); a phasing-out of diesel and introduction of cleaner vehicles; a ban on all traffic in central London; the scrapping of new road bridges and tunnels; more public transport; and better conditions for bicycles and pedestrians. Only these, say the reformists, will make London a modern city, fit for living in and bringing up children.

Future generations will surely look back and see early 21st century air pollution in London as one of many epidemics, like cholera, flu and TB, to have hit the city and eventually been dealt with. And just as the coal merchants fought King Henry’s ban on coal burning or the Clean Air Act of 1955, so today’s car-makers and drivers who are bitterly opposed to changing their habits will have to change their ways.

London has reached a turning point and there is only one, cleaner, direction that the city will be allowed to go.