On 25 June 2026, the UK recorded its hottest June day ever: 36.7C in Merryfield, Somerset, triggering a rare red warning for extreme heat from the Met Office.
The red warning, which warns of danger to life, was issued for southern, central and western England and parts of Wales until midnight on Thursday. It was later extended for a third consecutive day for London and parts of south-eastern England until 21:00 BST on Friday. This is only the second time the Met Office has issued a red heat warning since the alert system was introduced in 2021.
“What is a red heat warning? The UK's extreme heat alerts explained, with examples from the record-breaking June 2026 heatwave.”
Red is the highest level in the UK's three-tier heat-health warning system. It means population-wide adverse health effects are likely, leading to serious illness or danger to life. The warning also highlights substantial changes in working practices and daily routines, a high risk of failure of heat-sensitive systems (such as power cuts), and transport delays. During this heatwave, schools closed, a hosepipe ban was introduced in Kent, and train services were cancelled.
The extreme heat came as warm air from North Africa swept across Europe. Red warnings were also in place in France, Spain, Italy, Croatia and Poland. Landmarks such as the Eiffel Tower and the Louvre in Paris were shut. In the UK, all four nations recorded their highest temperatures of the year: England 36.7C, Wales 35.6C (in Cardiff, also its hottest June day), Scotland 31.2C, and Northern Ireland 30.0C. Overnight, the UK experienced its warmest June night, with Cardiff not falling below 23.5C, beating the 1976 record of 22.7C.
The background to these alerts is a growing recognition that heatwaves pose a serious health threat, particularly to the elderly and those with pre-existing conditions. The Met Office's warning system, developed with the UK Health Security Agency, uses colour-coded alerts (yellow, amber, red) to give the public and authorities time to prepare. The first red warning was issued in July 2022, when temperatures exceeded 40C for the first time.
Why it matters for UK readers:
If you live in an area under a red warning, you need to take immediate action. The Met Office advises staying indoors during the hottest part of the day, keeping curtains closed, drinking plenty of water, and checking on vulnerable neighbours. Transport may be disrupted – trains often run at reduced speeds or are cancelled to prevent tracks buckling. Power cuts can occur as demand for cooling soars. The NHS also comes under pressure: during this heatwave, at least six NHS trusts in England declared critical incidents. Hosepipe bans may be introduced to protect water supplies, as happened in Kent.
Key questions answered:
Q: What is a red heat warning? A: A red heat warning is the highest level of alert from the Met Office, indicating extreme heat that poses a risk to life. It is issued only when there is a very high probability of population-wide adverse health effects, serious illness, or danger to life, and when substantial disruption to daily life is expected.
Q: How does the UK's heatwave warning system work? A: The Met Office issues three levels of heat-health alerts: yellow (be aware), amber (be prepared), and red (take action). Red warnings are rare and trigger emergency responses from the NHS, local councils, and transport operators. Warnings are based on forecast temperatures and their likely impacts on health and infrastructure.
Q: What should I do during a red heat warning? A: Stay indoors between 11am and 3pm if possible, drink plenty of fluids, avoid strenuous activity, and close curtains to keep rooms cool. Check on elderly or vulnerable relatives and friends. Do not travel unless necessary, and be aware that train services may be cancelled or delayed. Follow advice from the NHS and local authorities.
What happens next:
Temperatures are forecast to ease over the weekend, with thundery showers moving in from Scotland and the south-west. The red warning for London and the south-east will end at 21:00 on Friday. However, amber warnings remain in place for parts of England and Wales. The Met Office and UKHSA will continue to monitor the situation and update alerts as needed.