Half the diesel and petrol cars in greater Paris will be banned from the road tomorrow in an attempt to reduce the health-threatening cloud of polluted air which has settled on northern France.

From 5am only odd-numbered cars will be allowed to drive in the Ile-de-France, unless they have electric or hybrid motors. Taxis, buses, emergency vehicles and cars carrying three people or more are exempted. All trucks are banned.

On Tuesday the ban will then apply to odd-numbered cars unless the weather changes. Foreign vehicles must obey the rules.

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Since last Wednesday, a run of warm, windless days and cold clear nights has clamped a lid of warm air over northern France. Minuscule particles of pollution from car exhausts, industry and agriculture have accumulated under that lid to dangerous levels.

The pollution is largely invisible and therefore not a “smog” or pea-souper fog of the kind which existed up to the 1970s. Paris enjoyed bright sunshine throughout the weekend.

There was, in fact, almost a carnival atmosphere. All underground and suburban trains and buses had been declared free to try to keep cars off the road. A light breeze reduced the pollution on Saturday and again yesterday.

Nonetheless, the level of official “pollution alert” – 80 microgrammes of tiny particles for every cubic metre of air – is likely to be exceeded again tomorrow and on Tuesday as the wind drops. The government decided on Saturday night to impose regulations on “alternate” use of cars which have not been triggered since 1997.

Motorists’ organisations complained that this was an overeaction and would cause enormous hardship to commuters. The government said that it it had no choice.

The health minister Marisol Touraine said: “Pollution is a public health issue. We were obliged to take tough action.”

France is especially vulnerable to this kind of pollution because it is 60 per cent dependent on diesel cars. In the 1960s, French government and industry made a strategic decision that diesel engines were less polluting and would gradually supersede petrol.

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The French car giants, Renault and Peugeot-Citroen invested heavily in diesel engines. Diesel fuel was taxed less heavily than petrol – and still is.

For nearly two decades France has been aware that this was a mistake. Diesel engines are more polluting, not less. Fumes from diesel cars, as well as industrial emissions and agricultural fertilisers, are blamed for increasing the micro-particles in the French atmosphere to dangerous levels.

Successive governments have shied away from increasing taxes on the diesel fuel which is used by two out of three motorists (and voters).

According to on study, there are 40,000 premature or unnecessary deaths in France each year because of the high level of atmospheric pollution. Other experts insist however that the scare has been exaggerated.

A French lung specialist, Professor Jean-Philippe Derenne, said: “In 50 years I have never come across anyone who died from air pollution. Between those people who smoke two packets of cigarettes a day and those people who walk in the streets of Paris, there is not the beginnings of a comparison.”