Brits are set to see temperatures ratchet up over the weekend by more than 10C in some parts and the mercury could hit 41C next Tuesday which would make it the UK's hottest day on record.
Extreme conditions are being predicted by the Met Office which has a yellow amber warning in place for heat that will run from Sunday until Tuesday.
People are being advised to take care under the oppressive weather and there is also anticipated to be an increased strain on hospital and train services.
Forecasters and weather maps have predicted that temperatures could rise into the high 30Cs and possibly low 40Cs with a WXChart map currently showing 41C for parts of eastern England.
Tuesday is likely to be the hottest day, with the potential to top the UK record temperature of 38.7C set in Cambridge in 2019.
BBC weather forecaster Sarah Keith-Lucas said: "We've seen a little bit of a lull in the heatwave conditions over the last 24 hours or so, it was a little bit fresher on Thursday and into Friday too.
"But intense heat is on the way, particularly by Sunday into Tuesday the Met Office have issued an amber warning for extreme heat across much of England and Wales, we are likely to see widespread impact from this spell of severe heat.
"Health impact not just for the vulnerable, we could see transport disruption, potentially disruption to energy supplies as well, so certainly some severe weather on the way with those exceptionally high temperatures Sunday to Tuesday."
On average, the mercury will remain in the mid-20s today, before rising to at least 35C in southern, central and eastern areas of England by Tuesday.
Hospital and train services are already under pressure from the heat, with the NHS facing a "surge" in demand from heat-related admissions, and Avanti West Coast has warned their services may be cancelled at the last minute.
Back to today and it will begin with outbreaks of showery rain moving south-east across northern and central areas of the UK.
Meanwhile, people in the South and South West can expect warm sunshine.
London is forecast to experience 26C on Friday, while 23C is predicted for Cardiff, 20C in Belfast and 19C in Edinburgh.
Saturday is also set to start with overcast skies and scattered showers in northern areas, before turning dry across the nation as the extreme heat moves in.
Cabinet Office minister Kit Malthouse has said the Government is preparing for a "surge" in demand on the NHS and other services due to the expected heatwave.
After chairing a meeting of the Cobra civil contingencies committee in Whitehall, Mr Malthouse urged the public to look out for people who were particularly vulnerable in the heat.
Avanti West Coast has warned passengers who wish to use services between London Euston and Scotland to plan ahead due to the impact of the heat on rail lines.
The company said that weekend services may be cancelled at short notice while journeys on Monday and Tuesday will be subject to amended timetables.
UK forecast for the next 5 days
Showery in the north. Fine and warm in the south.
Today:
Cloud and outbreaks of showery rain moving southeastwards across central parts of the UK. Turning brighter in the northwest later. Warm sunshine across the south and southwest.
Tonight:
Rain and showers clearing eastern England. Most parts dry with clear periods, a few fog patches possible. Cloud and patchy rain spreading into far northwest of Scotland later.
Saturday:
Cloud clearing during the morning across central and southern Britain to be warm and sunny. Remaining cloudier in north with outbreaks of rain in far north where breezy too.
Outlook for Sunday to Tuesday:
Early cloud and rain across Scotland should become confined to Shetland through Sunday. Elsewhere, sunny and increasingly hot. Likely hot or very hot, probably exceptionally so, for many Monday/Tuesday.
