On 25 July 2022 London declared a major incident as the city and much of the United Kingdom experienced an extreme heat wave that set national temperature records and strained public services. The UK Met Office issued its first-ever red extreme heat warning for parts of England, including London, forecasting prolonged temperatures above 40°C (104°F) — a threshold never before recorded in the country. Authorities mobilised emergency responders and public-health messaging to protect vulnerable residents. The heat was part of a broader European heat wave driven by a persistent high-pressure system and unusually warm air masses from the continent. The Met Office recorded temperatures exceeding 40°C at multiple sites, with the highest UK temperature on 19 July 2022 at 40.3°C (recorded in Coningsby, Lincolnshire); London itself experienced temperatures well above typical summer norms during the period surrounding the emergency declaration. Such extremes increased risks of heat illness, dehydration, worsened chronic conditions and heat-related deaths, particularly among older people and those without access to cooling. Health services reported elevated demand. The UK Health Security Agency and local NHS trusts issued guidance urging people to stay hydrated, avoid strenuous activity during the hottest parts of the day and check on vulnerable neighbours. Ambulance services and hospitals in London and elsewhere faced higher call volumes for heat-related conditions. Coroners and public-health officials later linked a substantial increase in excess deaths across the UK during the heat wave to the extreme temperatures; precise attribution and counting of heat-related fatalities involves complex analysis and, in some cases, remains subject to official investigation and reporting. Transport and infrastructure were also affected. Rail operators warned of speed restrictions and cancellations after tracks buckled in some areas, and road surfaces and airport operations experienced heat-related disruptions. The heat exacerbated air quality problems in some places, contributing to additional health hazards, especially for people with respiratory conditions. London’s declaration of a major incident triggered coordinated action across agencies, including the Greater London Authority, London councils, the NHS and emergency services. Cooling centres and outreach efforts were set up in parts of the city to provide relief for those without adequate cooling at home. Local authorities focused on safeguarding people in care settings and on the streets, including homeless populations who are especially exposed during extreme heat. The 2022 heat wave reignited public and political discussion about climate change and urban resilience. Experts and researchers pointed to the increasing likelihood of extreme heat events in the UK as global temperatures rise, highlighting the need for long-term adaptation measures such as heat-resistant infrastructure, improved housing insulation and access to cooling for vulnerable groups. The event also raised questions about preparedness for rare but high-impact weather extremes in regions historically not accustomed to such temperatures. Official inquiries and post-event reviews were later expected to assess the emergency response, public-health messaging and the factors contributing to excess mortality during the heat wave. While immediate emergency measures aimed to reduce harm, the 2022 episode underscored the challenge cities like London face in responding to intensifying climate-related extremes and protecting public health. Note: Attribution of specific deaths to heat is often complex and involves medical and statistical review; public agencies and coroners conducted subsequent analyses to quantify heat-related mortality linked to the 2022 heat wave.