"Air pollution is likely to rise significantly this weekend because of the warm, still weather and heavy holiday road traffic - leading the Government to issue a "summer smog" warning.

"People with breathing difficulties and parents of children with asthma are being especially urged to take precautions. Experts believe that levels of ozone and ultra-fine particles in the air that irritate the respiratory system are likely to rise with the daytime temperatures. A high-pressure system over England and Wales, combined with ample sunshine, is likely to bring the warm and still conditions over much of the country that can lead to a "high-pollution episode", said a spokesman for the Department for the Environment.

"Sunlight reacting with the gases released by car exhausts can generate ground-level ozone and fine particles called PM10s, which can irritate the lungs when inhaled, especially in people with pre-existing respiratory conditions."

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