A record-breaking heatwave across the United Kingdom has triggered a surge in life-threatening medical emergencies, with London’s ambulance service responding to its highest-ever number of critical calls on Wednesday. Temperatures reached 36.4°C in Yeovilton, Somerset, on Thursday, breaking the national June record for the second consecutive day after 36.1°C was recorded in Gosport, Hampshire, a day earlier.

The London Ambulance Service reported 642 Category 1 calls — the most serious, involving cardiac arrests or patients not breathing — out of 7,900 total calls on Wednesday, and crews attended nearly 3,600 patients. More than 400 additional ambulance crews were deployed this week, according to the service, which attributed the rise to heat-related fainting, breathing difficulties and heart problems. NHS trusts in affected areas declared critical incidents, and the UK Health Security Agency issued a red heat health alert warning that even healthy individuals faced a risk to life.

Transport networks suffered severe disruption. Over 10 motorists were hospitalised with heat-related illnesses after being stranded for hours on the M25 motorway, with one person airlifted due to dehydration, according to local emergency services. A double-decker electric bus caught fire in west London, and train operators urged passengers to avoid non-essential travel as speed restrictions were imposed. Schools across the country closed early, and a hosepipe ban was introduced in Kent amid record water demand. Animal welfare experts from the RSPCA advised dog owners not to walk their pets during the red warning and to call emergency services if they saw an animal trapped in a hot car.

The Met Office extended its rare red extreme heat warning for parts of London, south-east England and the east of England until 9pm on Friday, with temperatures forecast to reach 38°C in some areas. An amber warning remains in place for Saturday across the south-east. Forecasters said a change to cooler, more average temperatures was expected from Sunday, with London likely to see highs of 26°C. The London Ambulance Service said its crews continued to work in challenging conditions and urged the public to stay out of the sun and keep hydrated.