Health charities have said Britain’s heatwave could lead to “life-threatening” conditions, as the country recorded its hottest day of the year for a third day in a row. Northolt in west London reached the national high of 26.6C at 11.30am on Wednesday, beating the previous day’s high of 26.1C in Cardiff on the first day of meteorological summer. Eluned Hughes, the head of health advice at Asthma UK, said: “Soaring temperatures combined with high pollen levels can trigger asthma symptoms and could result in life-threatening asthma attacks. Hot weather can cause people’s airways to become irritated and inflamed, while hot air entering the respiratory system can trigger coughing and shortness of breath. It’s vital that everyone with asthma takes their preventer inhaler as prescribed.” The Met Office issued a yellow weather warning for thunderstorms for south-west England and south-west Wales for Wednesday morning and warned there could be could be some short-term loss of power and other services, with potential for poor road conditions and public transport delays. Heavy and potentially thundery showers were expected to move into north Wales and north-east into the Midlands, but other areas were expected to remain warm and dry. The Met Office meteorologist Alex Burkill said: “The thunderstorms could bring lots of lightning, some hail, as well as some heavy rain, and with the half-term there is an increased number of tourists in this area. The thunderstorms do then push north-eastwards into the Midlands and across more of Wales, but they also ease and break up, so these places will see some showers but they won’t be as intense.” Temperatures were expected to be a little lower on Thursday but with fine and dry weather for most, although a few thundery showers remain possible. The recent heatwave has come hot on the heels of a dismal May, where heavy downpours and prolonged spells of rain were a near constant for many throughout the month. The UK had its fourth highest amount of rainfall on record for the month, with an average of 120mm. England had its fifth wettest May on record and its wettest since 1967, with 111mm of rain. Wales experienced the wettest May since records began in 1862, with 245mm of rainfall, topping the previous record of 184mm set in 1967, according to the Met Office. Wales had its hottest day of the year on Wednesday, with 26.3C recorded at Hawarden, Flintshire.