The UK Health Security Agency (UKHSA) raised the alert level at 12pm on Thursday (July 11), with the amber warning remaining in place until 9am on Monday (July 14).
The change reflects growing concern that the hot weather will not only cause discomfort but could have serious consequences for health, particularly among vulnerable groups.
An amber alert now carries a risk score of 12, and signals significant impacts across health and social care services.
It means a real risk to life, especially for people aged 65 and over, those with underlying medical conditions, and others who may be vulnerable in the heat.
Health officials also warn that younger age groups may also be affected, and that demand on NHS and social care services is likely to increase significantly.
There are concerns that internal temperatures in hospitals and care homes could exceed safe thresholds, putting patients and staff at risk.
The heat is also likely to affect staff’s ability to deliver care, especially with possible transport disruptions, power demand issues, and medicine management complications.
People living independently in the community, especially in poorly ventilated homes, are at particular risk of overheating.
Officials also note that other sectors such as transport may begin to see impacts, with travel delays and overcrowding more likely.
The warning comes as temperatures in London hit 32°C today, with overnight lows expected to remain around 20°C.
The weekend is set to remain hot, with highs of 30°C forecast for both Saturday and Sunday, before dipping slightly to 28°C on Monday.
Pollution and pollen levels are also high, and UV exposure is rated as very high, adding further strain for people with respiratory conditions.
The amber alert follows earlier forecasts that had London under a lower-level yellow alert, which has now been escalated in response to the increasing risk of illness, hospital admissions and potential deaths caused by sustained high temperatures.
