Britons have been urged to stay inside as the UK braces for “ferocious” temperatures breaching 40C, and swathes of the country are now covered in the first ever red warning for extreme heat.

A national emergency has been declared amid the threat of severe disruption as schools close, hospitals cancel appointments and events are scrapped.

The last week has seen high temperatures across Britain, but Met Office forecasters issued a red warning for Monday and Tuesday in an indication that the mercury could soar still higher.

Experts say there is now an 80% chance a new temperature record could be set, topping the 38.7C (101.7F) set in 2019 and a 50% chance of highs hitting 40C (104F).

Read more: What a Level 4 heatwave means for the UK

In a stark and dramatic warning, Met Office boss Penny Endersby said in a broadcast: “The extreme heat we are forecasting right now is absolutely unprecedented.

“Here in the UK, we are used to treating a hot spell as a chance to go and play in the sun. This is not that sort of weather. Our lifestyles and infrastructure are not adapted to what is coming.

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“Please treat the warnings we are putting out as seriously as you would a red or amber warning for wind or snow, and follow the advice.”

Her warning was echoed by College of Paramedics chief executive Tracy Nicholls, who said the “ferocious heat” the UK is predicted to experience over the next few days could lead to deaths.

She told Sky News’s Sophy Ridge On Sunday programme: “This isn’t like a lovely hot day where we can put a bit of sunscreen on, go out and enjoy a swim and a meal outside.

“This is serious heat that could actually, ultimately, end in people’s deaths because it is so ferocious. We’re just not set up for that sort of heat in this country.”

The UK Health Security Agency (UKHSA) raised its heat health warning to Level 4 – a “national emergency” – on Friday.

Level 4 is reached when “a heatwave is so severe and/or prolonged that its effects extend outside the health and social care system”.

The Met Office has issued an amber warning for the majority of England, which extends to southern Scotland and Wales from Monday until Tuesday.

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The UK’s first red extreme heat warning has also been issued across a large part of England, from London to Manchester and York on Monday and Tuesday, with transport services expected to be disrupted on both days.

Read more: Why Britain’s cities need a radical overhaul

The blame for the extreme heat roasting the UK has been levelled squarely at climate change by various scientists.

Climate attribution scientist at the Met Office Dr Nikos Christidis has said Tuesday’s 40C prediction is a result of our changing climate.

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