The Met Office has warned the heatwave in the UK will bring thunderstorms to England on Tuesday, as they issued an unprecedented heat warning followed by a flood warning.

While the mercury could reach 33C (91.4F) between Tuesday and Thursday, the forecast is showing that thunderstorms may begin to develop in the south east of England this afternoon.

This comes after the Met Office issued its first ever "amber extreme heat warning", as the UK’s highest temperature of the year so far was recorded at Heathrow on Sunday, where it reached 31.6C (88.9F).

The thunderstorms are likely to bring large hail and lightning, according to the Met, as the public are warned of potential impacts to travel and power supplies. 

Meanwhile, the mercury will remain above 31C (87.8F) during the week, with forecasters suggesting the next few days could be the hottest of the year.

The Met’s first ever "amber extreme heat warning" covers a large part of Wales, all of south-west England and parts of southern and central England, and will remain in force until the end of Thursday.

Public Health England (PHE) also issued a heat-health alert, warning members of the public to take measures to stay cool and look out for vulnerable people.

On Tuesday, PHE extended their heat-health alert until Friday July 23, as the Met forecasted the hot weather to continue for a few more days.

The UK heatwave, in pictures

An RNLI Lifeguard watching as sunbathers enjoy the scorching hot afternoon sunshine on the beach at the seaside resort of West Bay in Dorset

Credit: BNPS

The hot sun burns off the sea mist at sunrise as a paddleboarder goes across Roker Harbour to Roker Lighthouse in Sunderland on Tuesday morning

Credit: Simon Woodley/SWNS

Children play in a burst water main on Harstbourne Avenue in Belle Vale, Liverpool

Credit: PA

Soaring temperatures causing fridge-freezers to fail

Britain’s soaring temperatures are sending fridge freezers into meltdown with more than 100 makes and models failing to chill food properly in the heatwave, consumer investigators warned on Tuesday.

Testing by consumer group Which? found many simply did not function efficiently when the kitchen temperature went above 30C (86F) as many homes will discover during the current hot spell.

All models sold in Britain claim to keep a stable temperature within right up to 32C (89.6F) outside but tests in those conditions by Which? over the years have found many struggled to cope.

Warmer fridge and freezers temperatures do not just mean finding out beer is less than ice cold, it can also lead to harmful bacteria breeding – a risk in particular to meat.

Which? said: "Chances are you’ll be counting on your fridge freezer in this warm weather. But if the beers are a tad more tepid than you’d hoped and the ice cream a little soft, it might be time for a new fridge freezer."

It added: "Among all the fridge freezers we’ve reviewed, we’ve found more than 100 that struggle to keep food safely chilled when the room heats up.

"The warmer the temperature in the fridge gets, the more likely it is that heat-loving bacteria will thrive."

‘Scuff your feet in shallows to warn off venomous fish’, says coastguard

Swarms of venomous weever fish armed with agonising stings are invading Britain’s baking beaches.

Barefoot walkers are warned to take extra care during the heatwave amid reports of painful seaside encounters.

Rows of poison-loaded spines along the tiny critters’ fins inflict an excruciating sting if stepped on.

Dubbed the country’s most poisonous fish, the creatures are hard to spot buried in the sand hiding needle-sharp barbs just below the surface.

A spokeswoman for the Maritime and Coastguard Agency said: “Our advice is for beach-goers to wear waterproof shoes or sandals in shallow water or around rocky areas and to scuff or stamp their feet to make creatures aware they are approaching

“Weever fish can be found along the UK’s shores during the summer months.”

Britain’s first ever ‘extreme heat’ warning issued

The Met Office issued its first ever "extreme heat" warning on Monday as it says Britons in parts of the UK are at risk of sunburn and dehydration.

The amber warning – which is similar to those issued when heavy rain or snow is forecast – covers a large part of Wales, all of south-west England and parts of southern and central England, and will remain in force until the end of Thursday.

The new Extreme Heat National Severe Weather Warning was launched at the start of June 2021, with warnings to be issued based on the impacts of extreme heat.

Amber and red warnings will be made to inform the public of potential widespread disruption and adverse health effects.

⚠️⚠️ Amber Weather Warning issued ⚠️⚠️

Extreme Heat across parts of South Wales, West Midlands, southern and southwestern England

Valid until 23:59 Thursday

This is the first ever Extreme Heat Warning issued#Heatwave

Latest info 👉
Stay #WeatherAware

— Met Office (@metoffice) July 19, 2021

What to expect and what should you do?

Here’s what to expect:

  • Adverse health effects are likely to be experienced by those vulnerable to extreme heat
  • The wider population are likely to experience some adverse health effects including sunburn or heat exhaustion (dehydration, nausea, fatigue) and other heat related illnesses
  • More people are likely to visit coastal areas, lakes and rivers leading to an increased risk of water safety incidents
  • Some changes in working practices and daily routines likely to be required
  • An increased chance that some heat-sensitive systems and equipment may fail, leading to power cuts and the loss of other services to some homes and businesses
  • Some delays to road, rail and air travel are possible, with potential for welfare issues for those who experience prolonged delays
  • And what can you do to stay safe?

  • Look out for those who may struggle to keep themselves cool and hydrated – older people, those with underlying conditions and those who live alone are particularly at risk
  • If you live alone, ask a relative or friend to phone to check that you are not having difficulties during periods of extreme heat
  • Close curtains on rooms that face the sun to keep indoor spaces cooler and remember it may be cooler outdoors than indoors
  • Drink plenty of fluids and avoid excess alcohol
  • Never leave anyone in a closed, parked vehicle, especially infants, young children or animals
  • Try to keep out of the sun between 11am to 3pm, when the UV rays are strongest and avoid physical exertion in the hottest parts of the day.
  • Your weather forecast

    Weather 20/07/2021

    Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.