A three-day heat alert has been issued as temperatures are set to rocket to 34C.
The warning covers parts of England from midnight on Friday until midnight on Sunday.
NHS England and the Met Office have issued a level two heat-health alert for the East Midlands, east of England, the southeast and the southwest, meaning there is a 60 per cent chance of heatwave during this period.
A level one warning covers parts of northern England, where the probability of heatwave conditions is 30 per cent, while there is a 40 per cent chance in the West Midlands.
Met Office deputy chief meteorologist Dan Rudman said: “Temperatures will continue to rise as we go through the week, becoming well above-average by Friday when many parts of the southern half of the UK are likely to exceed 30C and may even reach 34C in some places.
“This is the first spell of hot weather this year and it is unusual for temperature to exceed these values in June. Many areas will also see some warm nights with minimum temperatures expected to be in the high teens or even low 20Cs for some overnight.
“The heat is a result of a mix of homegrown warming in the day due to high pressure, as well as a southerly airflow introducing some of the warm air from the continent to UK shores.”
Agostinho Sousa, head of extreme events and health protection at the UK Health Security Agency, added: “Temperatures are forecast to reach 30C in some parts of the south on Friday and we want everyone to enjoy the hot weather safely when it arrives and be aware of good health advice for coping with warmer conditions.
“During periods of hot weather it is especially important to keep checking on those who are most vulnerable, such as older people and those with heart or lung conditions. Make sure to look out for signs of heat exhaustion and follow our simple health advice to beat the heat.”
From Wednesday onwards while cloud, rain and breezy conditions continue across the northwest, it will become increasingly warm in the south as high pressure builds.
This will bring settled conditions allowing temperatures to build day-on-day and for it to become warm, or even hot, for a time by Friday.
A UK heatwave threshold is met when a location records a period of at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold, which varies by county.
The highest temperature reached in the UK so far this year is 27.5C at Heathrow on 17 May.
