The lovely weather will make people want to leap into the nearest pedalo (Photo by Peter Nicholls/Getty Images)

A hot weather health warning covering all of England has been upgraded to amber, ahead of the mercury rising to a forecast 33C on Saturday.

Much of the UK is predicted to enter a heatwave over the next few days with the highest temperatures of the year so far.

The warning, issued by the UK Health Security Agency, says a rise in deaths is likely ‘particularly among those aged 65 and over or with health conditions’.

Internal temperatures in hospitals and care homes may also ‘exceed recommended threshold for clinical risk assessment’, the UKHSA said.

Every part of England is covered by the warning, which will remain in effect until 9am on Monday.

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Dr Agostinho Sousa, Head of Extreme Events and Health Protection at UKHSA, called for people to take ‘sensible precautions while enjoying the sun’.

He said: ‘The forecasted high temperatures are expected to be short-lived but could primarily impact those over the age of 65 or those with pre-existing health conditions.

‘If you have friends, family or neighbours who are more vulnerable, it is important to check in on them and ensure they are aware of the forecasts and are following the necessary advice.’

What do different colours of warnings mean?

The UKHSA uses four different colours to show how serious the threat from hot weather is: green, yellow, amber and red.

Which colour applies to a particular event depends on two things: its likelihood, and its impact.

For example, an incident with a likelihood of less than 30% and a ‘very low’ impact will be rated green, while an incident with a likelihood of more than 90% and a ‘low’ impact will be rated yellow.

An incident is rated amber if its impact is ‘medium’ and its likelihood is over 60%, or if its impact is ‘high’ and its likelihood is between 30% and 89%.

The only events rated red are those with a ‘high’ impact and a likelihood of 90% or more.

Those concerned about the heat are also advised to:

close windows and curtains in rooms that face the sun
wear suitable clothing, seek shade and apply sunscreen regularly if going outside
stay out the sun between 11am and 3pm, the hottest time of the day
plan outdoor physical activities for cooler times of day like morning and evening

Dr Natasha Fernando, medical director at Medichecks, also told Metro that milk can sometimes do more to hydrate you on a sunny day than water.

Workers from the City of London relax in the sunshine (Picture: Amer Ghazzal/Shutterstock)

Meanwhile, young people are being urged to stay away from rivers and lakes this weekend.

Firefighters warn the scorching weather can lead people to do risky things in the search of some relief, including taking a dip in dangerous waterways.

Rescuers have been called out to people who have found themselves stuck in mud, caught in a strong tide, or trapped in a capsized boat.

Londoners taking advantage of the warm weather to relax by the Thames (Picture: Amer Ghazzal/Shutterstock)

Pam Oparaocha, LFB’s assistant commissioner for prevention and protection, said: ‘With warm weather and school holidays on the horizon, we want people, especially young people, to enjoy our waterways safely, and that starts with education.

‘Strong currents, underwater hazards and cold water shock can be deadly.

‘It’s important to know the risks and to familiarise yourself with lifesaving equipment like throwlines, which are available along many of London’s waterways.’

Firefighters in Twickenham have been taking a hydraulic ‘river flume tank’ to schools and youth groups in the area to demonstrate how flowing water behaves.

London deputy mayor for the fire service Jules Pipe said the city’s waterways may look appealing in the heat, but they can contain ‘hidden dangers’.

She said: ‘As the hot weather continues and with the summer holidays looming, this timely work with young people will help save lives and build a safer London for everyone.’

Will there be a heatwave this weekend?

In order for a heatwave to be made official, the Met Office says several conditions must be met.

The peak temperature must exceed a certain level for at least three days in a row, and that level changes depending on where you are in the country.

In north and west parts of the UK, the threshold is 25C, while in Greater London and the Home Counties it’s up at 28C.

Met Office Deputy Chief Meteorologist Tony Wisson said: ‘Over the next few days, settled weather and warm sunshine will allow temperatures to rise day on day.

‘Temperatures will then rise further towards the end of the week as winds turn more southerly and even warmer air over continental Europe will be drawn across the UK.

‘We could very well see several places exceeding 30ºC, which will be the highest temperatures of the year so far.’