The alert is active from 12pm Thursday to 9am Monday, warning of a likely rise in deaths among vulnerable people.
Temperatures are expected to reach 31C on Thursday and Friday, peaking at 33C on Saturday, with similar high temperatures on Sunday.
All regions in England are at high risk, anticipating significant impacts across health and social care services.
Charities including the British Heart Foundation, Age UK, and Dementia UK have provided advice for vulnerable groups, emphasizing hydration and checking on older relatives.