An amber heat health alert has been issued for large parts of England.
A yellow weather alert has been issued for the rest of the country.
The alerts, issued by the UK Health Security Agency (UKHSA), are due to be in place from 9am on Tuesday, until 6pm on Wednesday.
Explainer: What is a heat-health alert?
The amber alert - described as an "enhanced hot weather response" - covers East Midlands, West Midlands, East of England, London, and the South East.
The UKHSA warns significant impacts are "likely" across health and social care services due to the high temperatures.
The yellow alert covers the North East, North West, Yorkshire, The Humber, and the South West.
Sky News meteorologist Christopher England said the high pressure that brought the warmth of the last few days via the "h