Healthy schoolchildren were kept indoors yesterday as government experts' conflicting messages about the dangers of smog led to widespread confusion.

The Department for Environment, Food and Rural Affairs warned of "very high" levels of pollution due to a mixture of dust from the Sahara and industrial emissions from Europe arriving on a south-easterly breeze.

But its own advisers at Public Health England admitted that the "vast majority of people" would feel no effects and independent experts said there was "no need" to stay indoors.

Photographs of the Prime Minister's official car coated in a thin film of dirt captured the public imagination following an air pollution alert issued by Defra earlier in the week.


However, a similar alert was put out three weeks ago with little or no fanfare, when pollution levels were higher in London than yesterday.

One possible reason that this week's pollution received so much more attention is that the Met Office took over responsibility for providing Defra with pollution forecasts on Tuesday.

Defra, which previously took its data from a private firm called Ricardo-AEA, had on Monday trumpeted its "improved" pollution forecasting service, giving earlier warnings and greater detail, which happened to come online as the Saharan smog hit. The worst of the pollution had dissipated last night, although levels will remain above normal for the rest of the week, before south-westerly winds blow the pollutants offshore.

Defra warned of 'very high' levels of pollution due to a mixture of dust from the Sahara and industrial emissions from Europe arriving on a south-easterly breeze. Photo / AFP

Defra used Twitter to issue regular updates on the smog cloud yesterday, saying there would be "high or very high air pollution for much of the south of the UK". Asthma sufferers and the elderly were advised to avoid strenuous exercise, and one of Defra's official advisers suggested children should stay indoors.

Prof Frank Kelly, the chairman of the Department of Health's committee on the medical effects of air pollution and a member of Defra's air quality expert group, said: "As a general response, this is a good approach as children tend to run around outside and therefore breathe deeper.

"Besides those children whose asthma may be exacerbated by pollution and who would then need to increase their medication, the main issue is related to pollution exposure on a chronic basis, as current evidence indicates that lung growth is restricted. If there is no subsequent catch-up lung growth, then this respiratory deficit is carried forward through life."

Yet Paul Cosford, the director of health protection at Public Health England, which also advises Defra, said while air pollution was a "serious issue" it should be kept in perspective. "It's a small number of days of very high air pollution levels," he said. "For the vast majority of people, they will suffer no harm as a result. We may notice sore eyes, coughs, sore throats and perhaps a little bit of a wheeze if we are taking physical activity outdoors."

With no official advice from the Department for Education, some schools kept all children indoors all day. Some areas reported more 999 calls for respiratory problems, including East Anglia, where pollution was 10 out of 10 on Defra's scale. East of England Ambulance Service said it had around a third more calls in the morning rush hour than normal.

Forecasters warned that the smog would blow north today, affecting the Midlands, the North West and Wales.