Temperatures are expected to rise by another 10 degrees in most of the territory England the load on hospitals and trains is increasing in the coming days.
The average mercury will stay in the low 20s on the last working day of the week, before rising to around 35C (95F) in southern, central and eastern England by Tuesday.
Hospital and rail services are already under pressure due to the heat NHS faced with a “surge” in demand from heat-related inputs and Avanti West Coast warned that their services could be canceled at the last minute.
The Metaburo has issued an “amber” extreme heat warning for most of England and Wales from Sunday to Tuesday.
Tuesday is likely to be the hottest day yet and could surpass the UK temperature record of 38.7°C (101.7F) set in Cambridge in 2019, forecasters said.
The warning says the weather could cause health problems for the general public, not just people vulnerable to extreme heat, which could lead to potentially serious illness or life-threatening conditions.
Friday will start with a patch of rain moving southeast across northern and central Britain.
Meanwhile, warm sun is expected in the south and southwest.
London is forecast to hit 26C on Friday, while 23C is forecast for Cardiff, 20C in Belfast and 19C in Edinburgh.
Saturday is also set to start with cloudy skies and scattered showers in northern areas before turning dry across the country as intense heat sets in.
During the peak of the heat on Tuesday, 36C is forecast in the capital, 28C in Cardiff, 26C in Belfast and 25C in Edinburgh.
Cabinet Minister Keith Malthouse said the government was bracing for a “surge” in demand for the NHS and other services due to the expected heatwave.
Chairing a meeting of Cobra’s emergency committee in Whitehall, Mr Malthouse urged the public to keep an eye out for people who were particularly vulnerable in the heat.
Avanti West Coast has warned passengers wanting to use services between London Euston and Scotland to plan ahead due to the impact of the heat on rail lines.
The company said weekend services could be canceled at short notice and Monday and Tuesday journeys would be rescheduled.