East Anglia and the East Midlands could be enjoying temperatures of over 30C this week but the mini-heatwave has triggered a health alert.
The Met Office said there was an “80% probability” of heatwave conditions between noon on Tuesday (30 June) and 6am on Thursday in parts of England.
Temperatures are set to soar as a swathe of roasting air sweeps in from northern France and Spain.
The forecast triggered a ‘Level 2’ alert with the Met Office warning: “Heatwaves can be dangerous, especially for the very young or very old or those with chronic disease.”
The Level 2 alert - calling for “alert and readiness” - is the third-highest warning that can be issued.
Graham Bickler of Public Health England said: “There is considerable evidence that heatwaves are dangerous and can kill.
“In the 2003 heatwave, there were 2,000 to 3,000 excess deaths [more than usual] in England. Across Europe, there were around 30,000 excess deaths.”
The Met Office said: “Temperatures are expected to build on Tuesday and into Wednesday, with the hottest day of the year so far expected on successive days this working week.”
Wednesday is likely to be the hottest day of the year so far, with temperatures soaring to 33C (91F).
A Met Office spokesman added temperatures should drop again on Thursday when severe thunderstorms are likely to hit central and western parts of the country, before climbing again ahead of the weekend.
Clive James, of St John Ambulance, added: “Extreme heat can be dangerous, particularly for the very young and old, but by being prepared you can spot the early warning signs and potentially be the difference between life and death in an emergency.
“Heat exhaustion and heat stroke are the most serious problems that can develop when the mercury soars so it’s essential that people can spot the signs, such as headache and dizziness, and get somewhere cool and rehydrated as soon as possible.”
AA spokesman Paul Watters advised motorists to carry water on long journeys and prepare for extreme temperatures to soften road surfaces.
He said: “Roads start to soften at about 27C and if the hot weather lasts they absorb the heat a bit like a storage heater.
“Road surfaces can become a bit like dough and this can lead to cracks and the surface of the road can start to give.”