People experienced breathing problems

Admissions were six times higher than normal. Most were people with hay fever who had never before experienced such breathing problems, it said.

This year, pollen counts across the country have been particularly high, contributing to the problem.

The Met Office said last Friday's storms may have exacerbated people's asthma, with London taking the brunt.

Favourable conditions

The figures are provisional, but suggest that North West London was the worst hit, with most A&E departments seeing a significant increase in attendances with asthma or difficulty breathing symptoms.

People with asthma should be aware that thunderstorms could trigger their asthma Karen Newell, asthma nurse specialist at Asthma UK

Out-of-hours doctors as far as Reading also saw a significant increase in people attending with similar symptoms and NHS direct also saw a significant increase, a spokesman said.

The Met Office issued a warning on Friday morning to a number of health care providers after noting conditions likely to come together to generate an event, such as tunderstorms and high pollen counts.

The areas at risk were London, the South east and East Anglia.

He explained: "The thunderstorms as they are developing are drawing up air over a large area.

CONDITIONS THAT INCREASE THE RISK OF ATTACKS High pollen counts High levels of air pollution High temperatures Preceding dry spell of 5-7 days Significant thunderstorms Source: Met Office

"This air includes pollen, and if it has been dry for a while there will be a lot of pollen lying around on surfaces which may also be drawn up into the cloud along with the air.

"Once in the cloud, ice forms on the pollen and the internal currents mean that the ice particles containing the pollen circulate in the cloud, going through several cycles of freezing, thawing and shattering. This shattering process breaks the pollen down into small particles. Then it starts to rain releasing the pollen with it in a narrow concentrated down-draught.

"Effectively the pollen has been made smaller and is now more concentrated. Smaller pollen is thought to be more allergenic.

"If you combine this with high levels of ozone or nitrogen dioxide, which appear to make the lungs more sensitive to allergens and may themselves also be an irritant, then you get significant increases in breathing difficulty problems."

Baby Anya was one of those ill over the weekend with breathing problems

Patrick Ladbury, a father of two from London, had to take his 14-month- old daughter to hospital over the weekend when she developed breathing difficulties for the first time in her life.

"The nurse said they had been snowed under over the weekend with asthma attacks and that they were close to calling an emergency situation because they had so many people coming in with breathing problems."

Patrick said he was told by staff that his daughter's breathing problems might have been triggered by the weather conditions.

Karen Newell, asthma nurse specialist at Asthma UK, said: "People with asthma should be aware that thunderstorms could trigger their asthma.

"They should keep their reliever inhaler with them at all times and consider increasing their preventive treatment in advance of expected thunderstorms, in consultation with their doctor or nurse.

"If they are worried about their asthma, they should contact their doctor or call the Asthma UK Adviceline on 08457 01 02 03."