Summer smog reaches dangerous levels as weather turns chaotic

From heat-haze and summer smog to outsize hailstones and flash floods: more topsy-turvy weather is on the way, Britain's forecasters say.

Air pollution has been worsening because of the current heatwave and reached potentially harmful levels yesterday in a number of locations across the country, especially in the South and East. Severe thunderstorms are likely in some places today, with torrential rain and even an outside chance of tornadoes.

The weather may play havoc with the tennis at Wimbledon and the Glastonbury Festival, but the sun is likely to return tomorrow.

Summer smog was a hazard in some areas for people with breathing difficulties yesterday, caused by a photochemical reaction which happens when sunlight acts on traffic fumes to produce a large amount of low-level ozone. When mixed with particulates – tiny particles of pollution from chimneys and diesel exhausts – the result is a brown haze that can cause severe problems for people with heart and lung disease.

The Government issued an official smog alert and Ben Bradshaw, the Environment minister, warned anyone vulnerable to take special care. "People sensitive to air pollution, such as those with heart and lung disease, should be aware of the heightened risk to their health so they can take sensible precautions , such as avoiding exertion outdoors on hot afternoons," he said.

"We can all help to reduce the current high levels of pollutants by avoiding unnecessary car journeys by walking, cycling and taking public transport instead.

"Air pollution is something that can affect human health. During the 2003 heatwave, it was estimated, on the basis of previous work, that up to 800 premature deaths may have occurred as a result of the poor air quality. Fortunately, such episodes are becoming less frequent and severe due to large reductions in pollution from vehicles and industry following tighter regulation in the last few decades."

The National Society for Clean Air (NSCA) added another precautionary note: in times of air pollution, go easy on the barbecue. "We don't want to be killjoys," said Tim Brown, NSCA deputy secretary. "Barbecues are part of the fun of hot weather. But we are all responsible for pollution, and can all avoid making things worse, so, before igniting the coals, check the pollution forecast in your area."

Today will be different, however. Weathermen predict thunderstorms, strong winds and a chance of tornadoes in parts of Britain. A PA WeatherCentre spokesman said the storms were likely to bring lightning and hailstones up to the size of golf balls.

Storms were expected to start moving into south-western and some southern parts of England and Wales last night. During today, Wales and north-west England are likely to have some prolonged outbreaks of rain, with occasional thunderstorms which may produce torrential downpours leading to local flash flooding, the spokesman said.

"This is a fairly potent situation developing. Winds in the upper atmosphere will be fairly strong, and this will promote the development of some severe thunderstorms.

"These may bring hailstones up to the size of golf balls, wind gusts up to 65mph, extremely heavy rainfall leading to local flash flooding, and possibly isolated tornadoes.

"With any thunderstorm, the main threat is cloud-to-ground lightning, and the storms are likely to be very electrically active. If a storm approaches, try to get indoors quickly, and do not stand under trees."

Local air quality can be checked at www.airquality.co.uk or by calling 0800 556677