Image source, PA Media

In 2019, MPs passed a law that committed the UK to a legally binding target of net zero carbon emissions by 2050.

Countries globally have agreed to meet this target, which scientists say is necessary to slow global warming and reduce the risk of severe consequences from climate change.

With the current heatwave bringing the issue into sharp focus, campaign groups are urging candidates for the Tory leadership to prioritise the environment.

A new leader cannot ignore the "vital importance" of curbing the climate and nature crises, Mike Childs, head of science, policy and research at Friends of the Earth said.

“We need climate action that goes further, and faster, so that the next generation has a world left to inherit,” he said.

Earlier, Ed Miliband, Labour's shadow minister for climate change, said rival Tory candidates are "running away" from net zero commitments and they appear to be "rowing back" on the legal commitment made.

The extreme temperatures we are witnessing are being caused by climate change driven by greenhouse gas emissions, the Met Office has reiterated.

Prof Stephen Belcher, the forecaster's chief of science and technology, says their research shows it is "virtually impossible" for the current records to be reached in an "undisrupted climate".

In a video posted on Twitter, external, he says if the UK continues with a trajectory of high-emissions we could see temperatures like this every three years.

Rising emissions of greenhouse gases like carbon dioxide (CO2) are caused by our burning of fossil fuels like coal, oil and gas, which trap heat in our atmosphere.

Prof Belcher explains the country is "already committed to a level of warming" and the extremes will get worse in the future.

He also calls for the UK to continue with its target to eliminate its overall emissions of greenhouse gases, a target known as "net zero".

You might remember that last summer something called a heat dome caused sweltering temperatures in Canada and the US.

Well, now Europe is experiencing one of its own. It’s sitting mostly over southern Europe - as our graphic shows.

A heat dome is a large mass of hot air that gets trapped by high pressure.

“It’s sat there, wobbling, sending wafts of hot air our way,” the Met Office told BBC News.

For now it appears “firmly anchored”, meaning that we could see more hot air could come our way for a considerable time.

The UK does have its own potential right now for high temperatures - dry soil, strong sun, and above-average sea surface temperatures.

But the Met Office says that the heat dome is driving most of the conditions.

The London Fire Brigade has said , externalthat around 25 firefighters are tackling grass fires in Croydon as the heatwave continues.

The wildfires are in Shirley Hills, a large park in the south London Borough of Croydon.

Earlier today, the London Fire Brigade said 175 firefighters were tackling a grass fire on Pea Lane in Upminster, east London.

It warned that smoke was blowing over the M25 as three hectares of a cornfield and some scrubland were alight.

Bob Dale
In Charlwood, Surrey

For just over an hour, this village held the provisional record for the UK's highest temperature.

Just before midday the Met Office said 39.1C had been recorded - that was exceeded by the figure of 40.2C at Heathrow Airport an hour later.

Katrina Fouda, who runs the Greyhound pub in the village, and said customers have been visiting to shield under her umbrellas.

"I've got builders next door and they keep popping in for ice cream and cold drinks. They're on a roof at the moment, so they're extremely hot."

She added: "I used to live in Egypt, so I'm used to it."

Outside of the unprecedented heat being recorded in and around London, searing temperatures are also being seen around the UK.

In Wales, Hawarden in Flintshire has reached 35.5C, still below the record mark of 37.1C set in the same place just yesterday.

In Scotland, Eskdalemuir in Dumfries and Galloway has reached 30C, which is just under 3C lower than the record mark set in Greycrook in the Scottish Borders in August 2003.

Image source, PA Media

Northern Ireland is much cooler currently, with 25.6C recorded in Killowen, County Down - below the record of 31.3C in Castlederg, County Tyrone, in July 2021.

Here are some of the notable marks hit in England so far today:

• Monks Wood, Cambridgeshire - 38.5C
• Sutton Bonington, Nottinghamshire - 38.5C
• Santon Downham, Suffolk - 37.9C
• Rochdale in Greater Manchester - 36.3C

Nick Miller
BBC Weather

Several weeks ago when some computerised weather forecasts began to indicate that the UK could see temperatures reach 40C for the first time, to be honest, it was hard for many of us to believe.

Across a range of forecasts there are always some which are seen as outliers and this is how this particular prediction was viewed. It was deemed highly unlikely.

Since then, the same forecasts maintained the possibility of hitting or exceeding 40C and others joined them until what seemed improbable became probable.

There is an element of shock at reaching 40C in the UK but really no one should be surprised. Scientists told us this day would come because of climate change and now it’s arrived, it’s likely to happen again.

Image source, Geograph

A man in his 20s has died at the Cotswold Water Park, Wiltshire Police say.

Police were called to the park, located on the Wiltshire/Gloucestershire border, shortly after 18:00 yesterday.

The man was pulled from the water and confirmed dead shortly afterwards, they said.

The death on Tuesday follows a number of similar deaths in open water in recent days during the heatwave.

A 14-year-old boy is believed to have drowned in the River Thames on Monday and a 16-year-old boy died in Bray Lake, near Maidenhead, Berkshire, the same day.

A 13-year-old boy drowned when he got into difficulty in the River Tyne in Northumberland on Sunday, and a 16-year-old boy died in Salford Quays, Greater Manchester, on Saturday.

Boris Johnson has been holding his last Cabinet meeting as party leader, and has addressed the heatwave. Schools, transport, and the NHS should stay open "as far as possible", he said.

He said that it was important to think back to the decision to open up the country after coronavirus, and balance the risk with the need to keep society open.

Tom Edgington
BBC Reality Check

Image source, PA Media

As we've been reporting, a new record temperature of 40.2C has been recorded at London's Heathrow Airport, with the heat expected to intensify throughout today.

The transport hub often tops the temperature charts - in 2019, it briefly broke the UK record for July's hottest day ever at 36.9C, before Cambridge achieved 38.7C.

But why is the airport such a magnet for hot weather?

According to Paul Williams, professor of atmospheric science at the University of Reading, the "urban heat island" has a major impact on temperatures in Heathrow.

This is the process where buildings absorb more sunlight than open fields, and as cities tend to hang on to the heat for longer, this can push up temperatures by a few degrees.

Williams explains that Heathrow - with its large black asphalt runways and airport buildings - will naturally absorb more heat.

Read more.

Carol Kirkwood
BBC Weather Presenter

Have you ever wondered why your garden or car thermometer often reads differently from the forecast temperatures?

Often your thermometers will be exposed to sunshine for lengthy periods during the day.

That causes the mercury to shoot up. But what is actually happening is the sun is warming up the surface of the thermometer, which gives a reading of the thermometer temperature rather than the air temperature.

In order to be able to compare temperatures, we need to ensure they are all measured in a consistent way in a standardised environment. This is done universally using a Stevenson Screen and the set-up is the same around the world.

You may have seen these dotted around - they look rather like a beehive from the outside.

These screens stand at a certain height above the ground, are painted white, and are slatted to allow the free passage of air.

The thermometer, along with other meteorological instruments, are kept inside, in the shade.

The BBC's Matt Taylor talks us through what to expect as the day goes on.

The Met Office red warning for extreme heat remains in place, and some parts of the UK could see record highs of up to 42C (107.6F).

There's some relief from the heat on Wednesday, but not by much, he says.

Image source, PA Media

If you're just joining us or need a recap, here's a look at the situation across the UK:

• The UK is experiencing its hottest day on record, with the temperature reaching 40.2C at Heathrow, according to provisional Met Office figures
• Network Rail has issued a "do not travel" warning for people travelling through the "red zone" of the Met Office's weather warning
• Age UK has warned older people are more at risk from overheating and dehydration and has urged the public to check in on elderly friends or relatives
• Police have warned about the risks of swimming in open water after a number of people died trying to cool down in the heat
• There have been warnings of pressure on hospitals and ambulance services as temperatures rise with more call handlers put in place to deal with a surge in 999 calls

The Met Office says London Heathrow reported a temperature of 40.2C at 12:50 today.

It's a provisional record, it says, and temperatures are still climbing.

Just over an hour ago, a new provisional record of 39.1C was recorded at Charlwood in Surrey.

Until today, the record temperature for the UK was 38.7C, set in Cambridge in 2019.

Sam Gruet
BBC Newsbeat's cost of living reporter

Image source, Rex/Shutterstock

With energy bills sky high at the moment, it’s a question many of you may be asking yourself as you plug in your third or fourth fan.

But the website Money Saving Expert has been crunching the numbers. It found a typical desk fan costs just 1p an hour to run based on the current average standard electricity prices - so about 10p if you left it on all night.

A big tower fan doesn’t cost much more at about 1.5p an hour. Even a large floor fan typically costs up to 3p an hour, so about 72p if you had to run it all day and night - which in this heat, might not be a bad idea.

Emily McGarvey
BBC News Live reporter

Image source, Getty Images

Older people are more at risk from overheating during hot weather, which can lead to heat exhaustion and heat stroke - especially those who live alone or have long term health conditions.

Age UK recommends regularly checking in on the older people in your life - friends, family or neighbours - and offering to pop out to get anything they need so they don't have to go out in the heat themselves.

Health conditions that affect the heart, lungs and circulatory system make it more difficult to regulate temperature, and the body has to work harder, which can put strain on the heart.

"Those with Alzheimer’s or dementia, or severe mental illness, may struggle to remember to change their behaviours or to stay hydrated," says Jenny Lippiatt from Age UK's health team.

"While older people might drink teas and coffees throughout the day, we are encouraging them to stick to water, as they can become dehydrated more easily."

Age UK also recommends staying inside, having cool baths and showers, eating food with high water content and keeping spaces cool by drawing the curtains.

Pallab Ghosh
Science correspondent, BBC News

Image source, PA Media

The temperatures are likely to lead to roads softening this afternoon, because their asphalt surfaces are a magnet for heat.

But this shouldn’t cause too much of a problem for motorists today - at worst it will cause some parts of the road surface to deform slightly, creating a few extra bumps and grooves.

But in the long term, with heatwaves likely to occur more often, it will lead to damage to the road network and so increase the need for more regular maintenance.

Engineers are looking at ways to improve the materials used on roads to cope with the country’s changing climate.

But it is a fine balancing act, as the roads also have to be able to deal with wet and freezing weather.

A change that might make surfaces more resilient to heat, might also make them more vulnerable to winter conditions.

Nick Miller
BBC Weather

It’s all about the numbers today and just how high temperatures are going to go, but here are few words of caution about when we will know for sure what the maximum is.

Across the UK there’s a network of official Met Office weather stations with thermometers that have been verified to be as accurate as possible. Some of these send their readings automatically every hour. The data from others can come once or twice a day or even only once a week.

Even then, with significant readings such as a possible new record for the UK, there is a further verification process that takes place just to double check everything with the weather station is as it should be. That’s why temperature records are often referred to as provisional until they are properly verified.

We will know a number later today but there is always a possibility this could be surpassed with new information that arrives in several days. There is a much smaller possibility it could be discounted.

Michelle Roberts
Health editor, BBC News online

Image source, Getty Images

We tend to sleep best when the temperature around us is between 15 and 21C (60-70F).

Being hotter than this can make it uncomfortable.

When the body gets hot it will try to cool down by sweating and diverting more blood to the skin.

Sweating can leave us thirsty and dehydrated.

It’s worth taking some water with you to bed in case you need it. If you feel like you are overheating, you might want to take a cool shower or bath, or use some cold flannels and a fan if you have one.

A baby can’t let you know if they are too hot or too cold so it is important to monitor their temperature.

Read more.