Brits struggled to buy air conditioning units today as the country braced for its third heatwave in six weeks after the Government issued another health alert.Shops are sold out after homeowners bought the units to keep cool during the May and June heatwaves which brought the hottest days on record for both months.And those searching for one on sale today were left disappointed with people having already snapped them up before the next heatwave which begins this weekend.All three of the Which? best buy units were sold out on manufacturers' websites, and the £150 Lidl device which led to huge queues last week remains unavailable.DeLonghi is out of stock on all nine units ranging from £460 to £1,000, while the Currys boss warned AC supplies were 'pretty tight' ahead of the next heatwave.Alex Baldock revealed today that units have been 'flying off the shelves', with AC sales up 330 per cent over the latest heatwave weekend compared to a week earlier.The chief executive claimed that Currys was 'working incredibly hard to make sure we have got a healthy level of stock', adding: 'We are benefiting from being number one in the market and if anyone is going to have it, we are going to have it.'In France, people fought at Lidl after the chain promised to put 200,000 fans and AC units on shelves - with shoppers resorting to violence to ensure they got one.Enquiries to companies installing AC have been soaring, with Aervue Air Conditioning in Birmingham saying sales had doubled since March and business was 'manic'.It comes as Britain faces more drowning deaths and a 'risk to life' during the third heatwave of the year, after the country's hottest May and June days on record.The UK Health Security Agency (UKHSA) has issued a yellow health alert for southern and eastern England and the East Midlands from Saturday until Wednesday.The five-day alert warns of 'greater risk to life of vulnerable people' and that 'water‑ related incidents may increase, including risks from cold water shock and drowning'.The heatwave could also bring 'increased use of healthcare services by vulnerable people' and 'increased potential for indoor environments to become very warm'. TOP TEN HOTTEST DAYS IN BRITAIN - INCLUDING TWO LAST WEEK 1 40.3C July 19, 2022 Coningsby, Lincolnshire 2 38.7C July 25, 2019 Cambridge 3 38.5C August 10, 2003 Faversham, Kent 4 38.2C July 18, 2022 Pitsford, Northamptonshire 5 37.8C July 31, 2020 London Heathrow 6 37.7C June 26, 2026 Lingwood, Norfolk 7 37.1C August 3, 1990 Cheltenham, Gloucestershire 8= 36.7C August 9, 1911 Raunds, Northamptonshire 8= 36.7C July 1, 2015 London Heathrow 8= 36.7C June 25, 2026 Merryfield, Somerset Health officials fear further deaths after at least 11 people died in water-related incidents during the June heatwave – on top of the 17 during the May heatwave.Temperatures for the next few days are expected to be just below the heatwave threshold, with highs in London of 26C today and tomorrow and 27C on Saturday.But 29C is expected in the capital on Sunday - above the required 28C heatwave threshold. It will then be 30C on Monday, 28C on Tuesday and 29C on Wednesday.The Met Office defines a heatwave as three days in a row with daily maximum temperatures meeting or exceeding the heatwave temperature threshold.The threshold varies between 25C in Scotland, Northern Ireland, Wales and south-west England, and 28C in London and its surrounding counties.Today is set to see patchy rain clearing the far south, before sunny spells will develop elsewhere, with the North East staying breezy.Unsettled conditions are then expected from tomorrow in the North, but the weather is forecast to be increasingly warm further south.Met Office meteorologist Annie Shuttleworth said an area of high pressure building from the Azores will 'dominate our weather at least through much of next week, bringing plenty of dry and settled and sunny weather'. People enjoy a sunny day on the beach in Bournemouth in Dorset today as temperatures rise The Met Office forecast for London suggests temperatures of 28C will be met from SundayShe added: 'It is going to warm up day on day with high pressure staying in place. But with westerly winds, temperatures are not expected to breach the peaks that we saw through the June heatwave.'And it's also not quite as hot across western areas of Europe as that heatwave has pushed off into more eastern areas of Europe.'So although we are expecting heatwave conditions to develop across the UK by early next week, particularly across the South, we are not expecting the exceptional temperatures that we saw through late June.'Allergy UK warned people living with asthma or hay fever could experience 'thunderstorm asthma', which occurs when thundery weather causes high winds to bring pollen and pollution into the atmosphere, which can then be inhaled deep into the lungs, triggering or worsening asthma symptoms.Amena Warner, head of clinical services at the charity, said: 'Most people with hay fever will experience their normal range of symptoms – sneezing, runny nose and itchy eyes, but these will be more extreme.'However, more worryingly, hay fever can cause asthma symptoms to worsen and thunderstorm conditions can cause even mild symptoms to become severe, such as difficulty breathing and chest tightening.'For anyone affected by asthma and hay fever, it's important to be prepared and diligent in taking allergy treatments and medications to manage symptoms.'Anyone who experiences difficulty breathing should seek medical help without delay.'The charity said people can reduce the risks related to thunderstorm asthma by staying indoors before, during and after the storm, wearing a mask when outdoors to reduce pollen exposure, taking their usual medication, keeping a reliever inhaler with them and monitoring their asthma in case it deteriorates. The UK Health Security Agency issued a yellow heat health alert from Saturday to Wednesday The heatwave threshold is defined as three consecutive days at or above a set temperatureThe UKHSA's new alert comes after a sweltering heatwave last week, during which the Met Office issued a rare red warning for extreme heat for parts of the country and the UKHSA put red heat health alerts in place.The UK set a provisional June temperature record of 37.7C on Friday in Lingwood in Norfolk, according to the Met Office.It beats the previous June record for the UK of 35.6C dating back to 1976 by more than 2C.Last week also saw two of the UK's top ten hottest days on record – one being the 37.7C and the other a 36.7C high at Merryfield in Somerset last Thursday.In addition, last month was provisionally the warmest June in England since records began, as well as the second warmest for the UK.The average temperature in England across the month was 17.1C, beating the previous June record of 16.9C set last year.It means England's top three warmest Junes since data began in 1884 have all occurred this decade, with 2026 in first place, 2025 second and 2023 (16.7C) third.The mean temperature across the UK was 15.6C, ranking behind only 15.8C in 2023.Last month also saw a provisional new June record for the highest overnight minimum, with temperatures at Cardiff Bute Park dropping no lower than 23.5C on June 25.This year has also seen the highest May temperature on record, with 35.1C measured on May 26 at Kew Gardens in London.England and Wales both experienced their warmest spring on record in 2026, thanks partly to the heatwave in late May.