IT is the temperature, say data scientists, when dehydration hospital admissions go through the roof.

And it has already hit London.

The UK capital baked at 33C yesterday as another brutal and dangerous heatwave spread across Europe.

Glasgow and Edinburgh are today expected to swelter in a more manageable 28C. The mercury in Scotland rarely gets to 33, the all-time record, set last year, is 33.2C.

Southern and eastern England, the Met Office warned, could cook at a record 39C today, smashing a previous UK high of 38.5C.

This has serious health implications. Analysts at a firm called Draper & Dash crunched numbers for hospital admissions for dehydration.

It found that at 31C+ they rose 22.7% among the general population, and 33.3% for the elderly.

But at 33C they jumped 127% among the general population and 150% for

the elderly

Orlando Agrippa, the firm’s chief executive, said: “Think about the impact this has on hospitals across the country. They are already under severe strain, with shortages of beds and staff.

“To then deal with a sudden influx of ‘unplanned’ cases, leads to further pressure to manage beds, patient flow, and resources.”

Network Rail has warned train speed restrictions may be introduced in areas where tracks are at risk of buckling.

There are particular concerns over the heat at night – with dark not bringing respite.

The highest overnight average temperature (between 9pm and 9am) ever seen in the UK was 23.3C at St James Park in July 1948, and there

is a possibility this will be beaten

this week.

The average daytime temperature for the UK in July is 19C, which is already being exceeded by evening conditions this month.

On Tuesday night into yesterday the mercury hit 21C at St James Park.

The hottest ever temperature for July was recorded at 36.7C at Heathrow on July 1 2015.

The only place in Scotland where temperatures look relatively cool is northern Scotland.

Aberdeen is set to enjoy 20C today and 24C tomorrow.

France, which suffered thousands of deaths in a heatwave in 2003, is in its second canicule or extreme temperature event of the summer.

There are amber alerts for 40C temperatures in place. Paris is bracing itself for temperatures to rival a record of 40.4C set in 1947. Meteorologists, however, do not expect southern France to once again endure a 46C all-time high recorded last month.

Heatwave after heatwave is weakening the French.

“There is a fatal cumulative effect, especially for fragile people,” Serge Smadja, secretary general of SOS Médecins told Le Parisien.

“More than 1,000 firefighters were battling a major wildfire amid scorching temperatures in Portugal on Monday, where forest blazes wreak destruction every summer. Repetition of these episodes is more dangerous.”

In Germany, fish have died in dried up rivers, with western parts of the country expecting to top 40C yesterday.

“If these predictions are met, this heatwave would go down in the history books,” a spokesman for German weather service DWD said, according to English-language newsite The Local.

“As a meteorologist, I have never seen anything like this before.”

Recent weeks have also seen major wildfires in Spain, Greece and Germany.

EU authorities have warned that wildfires are “a growing menace” across the continent.

Large areas of central and northern Portugal are covered in dense,

unbroken stretches of forest on

hilly terrain.

Environmentalists have urged the government to limit the area of eucalyptus, which burns like a torch.

But it is a very valuable crop for Portugal’s important paper pulp industry, which last year posted sales worth £2.4 billion.