Sky-high pollen levels this weekend could spark deadly asthma attacks.
Experts said more than three million people in the UK have breathing conditions which could flare up as the temperatures begin to soar.
Dr Andy Whittamore, of Asthma and Lung UK, said: “These attacks can leave people fighting for breath, which can be terrifying.
“When pollen levels are at their highest this can be deadly for those with lung conditions, like asthma, who can suffer serious symptoms and have life-threatening attacks.
“People should check pollen and air pollution forecasts in their local area, so they can avoid going outdoors as much as possible on high pollen days.”
The medic also advised people to use preventer inhalers to reduce airway swelling before it starts – and to carry reliever inhalers to relax muscles if pollen levels rise suddenly.
Britain will slap on the sun cream during a five-day “Bermuda Bake” next week as the mercury hits the mid to high-20s. Tropical air driven by a weather pattern known as a Bermuda high will sweep in from Sunday.
Jim Dale, meteorologist for British Weather Services, said: “It is looking like the warmest spell of weather so far this year and can certainly be called a mini-heatwave.”
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The south and east will experience the best of the heat, with temperatures of up to 27C. But as the mercury rises, so will pollen, causing misery for hay fever sufferers and those with more serious breathing conditions.
Nearly 30,000 are killed from chronic obstructive pulmonary disease each year, while almost 1,500 people die from asthma attacks.
Former footballer David Beckham, 47, U2 singer Bono, 62, and Hollywood actress Sharon Stone, 64, all suffer from asthma.