Most of England has been issued a heat-health warning, with temperatures expected to reach 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.
According to the Met Office, temperatures in southern England and south-east Wales hit 30 degrees Celsius on Monday.
The heat follows what has been widely recognised as a summer of terrible weather for much of the United Kingdom.
While July was wetter and cooler than average, with maximum temperatures failing to surpass 20 degrees Celsius on a regular basis, the previous month was the UK’s hottest June on record.
Temperatures are anticipated to reach 31 degrees Celsius on Tuesday.
“We will see good sunny conditions through the week with cloudless skies, and some high temperatures by the time we get to Wednesday and Thursday, where we could see 31, maybe 32C,” Met Office spokesman Oli Claydon told the PA news agency.
The Met Office said that tropical storms in the far western Atlantic, as well as deep areas of low pressure, have helped to amplify the jet stream – a fast wind high in the atmosphere – over the Atlantic Ocean. This has led to high pressure “dominating over the UK”, it said.
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.
Conditions could change over the weekend, and Mr Claydon said there was “no indication at the moment of another strong heatwave after this”.