Temperatures topped 30 degrees Celsius on Monday.

Millions of Britons have already been suffering in the sun, as the hottest weekend of the year caused widespread air pollution and some major traffic jams.

The BBC's Robert Piggott: "High levels of ozone could cause health problems"

Weathermen said blistering conditions across the country had resulted in the highest temperatures of the summer so far.

According to weather forecasters, the tropical heatwave is set to make July the driest for 130 years.

Doctors have warned asthma sufferers to stay indoors and seek medical help if they suffered extreme symptoms.

Doctors have warned about the strength of the sun's rays

A spokeswoman for the National Asthma Campaign said: "Hot weather can be a particularly difficult time for asthma sufferers and others because of the accompanying air pollution and high ozone readings.

"Ozone is particularly dangerous because it can trigger asthma attacks. We are advising sufferers to check their equipment, stay inside, seek advice from their GPs and seek medical help if they experience an extreme attack."

Doctors also warned sunbathers to limit their exposure to the sun's rays and to drink plenty of fluids to avoid dehydration.

Traffic gridlock

Over the weekend, the lure of the sun proved too much for many drivers who headed straight to the beach determined to make the most of the weather.

Roads out of the major cities and towards the coast were generally busy with severe problems in the south west.

But the combination of heavy traffic and humidity increased levels of pollution enough for the government to issue smog warnings as levels of ozone and particulate matter began to rise.

There were high readings of ozone from London to Cardiff.

Monitoring centres run by the Department of the Environment recorded high levels of ozone in Cardiff, south Somerset, Wicken Fen in Cambridgeshire, Thurrock in Essex and areas of west London.

Large cities in particularly are viewed as hazardous areas for asthma sufferers. Particulates from exhaust causes smog to develop, and there is little wind to blow it away.