By Jason Taylor, April 1, 2014
A deadly pollution cloud that could prove fatal for people with serious heart and lung problems will sweep into the UK tonight and cover much of the country tomorrow.
As this terrifying map from the Met Office shows, huge swathes of the UK will suffer extraordinarily high levels of air pollution in the next 24 hours - hitting highest possible level 10 on the official warning scale.
The midlands and the south are set to be worst affected, but almost all of England and Wales will experience extremely high levels of dangerous pollution.
Clean air campaigners claimed the Government had tried to bury news of the sudden - and shocking - decline in air quality.
Maria Arnold from ClientEarth said: "In Paris, people have been offered free transport, but the Government here has been very quiet as they don't want to draw attention to this."
A 'perfect storm' has developed with light winds over the UK leading to a build up in pollution. At exactly the same time, dust from the Sahara is being picked up in vast quantities by very strong winds over Africa and propelled towards us.
The forecast from the Department for the Environment, Food and Rural Affairs (Defra) warns: "The current elevated pollution levels over parts of the UK are caused by light winds allowing the build up of pollution, plus dust from the Sahara contributing to pollution levels.
Friends of the Earth pollution campaigner Jenny Bates said: "Air quality in Britain is a national disgrace, with tens of thousands of people dying prematurely each year.
"Strong and urgent measures are needed to end this scandal, including action on road traffic, the cause of most pollution."
More than 29,000 people are die prematurely every year from small particles in air pollution, which can cause cancer.
Defra warned that adults and children with lung problems, adults with heart problems, and older people should avoid strenuous physical activity tomorrow.
People with asthma may find they need to use their reliever inhaler more often.
They advised reducing physical exertion, particularly outdoors, especially if you experience symptoms such as cough or sore throat.
"Anyone experiencing symptoms should follow the [official] guidance."
Defra claims that that overall levels of sulphur dioxide have fallen nearly 10-fold, and smoke levels 20-fold since the 1960s, as average air quality has improved.
The dangers caused by coal-burning power stations responsible for winter smog have decreased substantially, and road transport has become the biggest source of air pollution in most areas.
But rare occasions when dangerously high levels of ozone, nitrogen dioxide, sulphur dioxide, PM2.5 and PM10 particles - which can seriously damage human health - do occur.
The Great Smog of 1952 has been linked to the deaths of 12,000 people. A further 100,000 suffered respiratory illnesses.
It was the worst air-pollution event in the history of the UK and led to several changes in practices and regulations, including the Clean Air Act 1956.
The World Health Organisation said last month that - more than 60 years on - air pollution is now the planet's biggest environmental health risk, causing seven million deaths a year - a figure that is on the rise.
Britain is already facing record fines of up to 300m annually after the European Commission claimed ministers had failed to reduce "excessive" levels of nitrogen dioxide in traffic pollution, despite 15 years of warnings.
* Anyone concerned about their health or that of a loved one tomorrow should call the Government's Air Pollution hotline on 0800 55 66 77