Commuters walk over London Bridge during warm weather in London, Britain
Most of England has been given a heat-health notice, with temperatures expected to hit 32 degrees Celsius (89.6 degrees Fahrenheit) midweek.
The UK Health Security Agency has issued a yellow alert for seven districts until 21:00 BST on Sunday.
It implies that the elderly and those with pre-existing medical issues should exercise additional caution.
The scorching weather will be felt across Wales, as well as portions of Scotland and Northern Ireland, where “unseasonably high temperatures” are expected.
London, the South East, the South West, the East and West Midlands, the East, North West, and Yorkshire and Humber are all covered in the alert.
Temperatures reached 30C on Monday in southern England and south-east Wales, according to the Met Office.
The hot weather comes after what has generally been regarded as a summer of poor weather for much of the UK.
While July in particular was wetter and cooler than average with the maximum temperature failing to regularly reach 20C, the previous month was the UK’s hottest June on record.
The warm conditions will continue through Tuesday with highs of 31C expected.
The forecaster added that temperatures could also hit 31C on Friday, although there could be more cloudy weather and chances of rain in the far north-west of Scotland.
Average temperatures are expected to return by the middle of next week.
Heatwaves are becoming more likely and more extreme because of climate change.
Last year the UK recorded temperatures above 40C for the first time. Scientists said that would have been “virtually impossible without climate change”.
