Britain faces mobile phone blackouts and nuclear shutdowns on Monday – as a 500 mile-wide "African hairdryer" brings record 41C (106F) heat hotter than Egypt.
Sunday's 33C beach rush is followed by up to 41C on Monday and Tuesday amid “brutal” heat from Africa, as shown on a weather map.
Phone networks are set to crash in some areas, with power cuts and even nuclear power station stoppages on the cards as extreme heat frazzles masts, wires and power plants.
The Met Office said: “There is a high risk of failure of heat-sensitive equipment, potentially leading to localized loss of power and mobile phone services.”
Experts Cornwall Insight said: “Increased temperatures can increase degradation of transformers and overhead lines, which could lead to failure.”
The Heatwave Plan for England said: “Nuclear reactors can trip out at above 40C. Rising temperatures cause problems for power stations as they are unable to cool components.”
And old bangers were told to stay off the roads. The AA says not to risk a beach trip in an old vehicle – as cars over 10 years are more likely to break down in the heat.
Temperatures will be up to 18C above average 23C summer highs and hotter than 37C Cairo, Egypt.
The Weather Outlook forecaster Brian Gaze said: “It’s heat on steroids. Temperatures look brutal.”
The Met Office said: “There is a 50 per cent chance we could see temperatures top 40C - and 80 per cent we will see a new maximum temperature reached. Exceptional temperatures are likely.”
Britain’s hottest temperature ever recorded is the 38.7C (101.7F) on July 25, 2019, in Cambridge.
The biggest beach rush of the year this weekend saw many B&Bs sold out.
As the UK braces itself for the peak of this month’s record-breaking heatwave Kit Malthouse, the Chancellor of the Duchy of Lancaster is chairing an emergency Cobra meeting at No.10 Downing Street to discuss the national response.
A national emergency has been declared after the Met Office issue its first ever red extreme heat warning, with temperatures predicted to reach 40C (104F) in some areas on Monday.
Meanwhile, caretaker Prime Minister Boris Johnson has left the capital and is reportedly set to host a party at Chequers.