Passengers are being warned to avoid non-essential travel - but if you do need to make journeys in the hot weather, here are some tips:

• Carry water with you and stay hydrated. Water fountains are available at some stations - ask staff if you need help locating one.
• Check journeys before setting off for delays or cancellations. A number of operators have reported disruption and limited services.
• Wear light, cool clothing and consider having a handheld fan.
• Don't forget to charge up any essential devices, as power supplies could be impacted too.
• If you feel unwell, do not travel - and seek assistance from staff if you become sick during your journey.

Barra Best
BBC News NI weather presenter

Northern Ireland is officially in the grip of a heatwave, but thankfully a much cooler one.

For the third day in a row the temperature dial has hit 25C, this time in Castlederg in County Tyrone.

The heat is expected to peak tomorrow though, rising close to a more uncomfortable 30C in some parts.

That would come close to Northern Ireland’s highest temperature on record, which is 31.3C set in July 2021.

It'll be a similar story in the Republic of Ireland where a record almost 140 years old could be threatened - 33.3C was recorded at Kilkenny Castle on 26 June 1887.

The Irish weather service, Met Éireann, issued a yellow heat warning from noon on Tuesday until 09:00 on Friday.

In England, a new UK June record was hit today in Gosport, Hampshire, with 36.1C.

In Wales, the mercury has hit 33.3C in Cardiff Bute Park, topping yesterday's maximum for the nation.

Scotland's highest temperature has been 27C in Charterhall, while Northern Ireland has seen 25.5C in Castlederg. Though neither have experienced temperatures as high as Tuesday, when they both recorded their hottest days of the year so far.

Image source, BBC Weather Watchers/@KWR

Charlotte Hadfield
Live reporter

This was the scene at London Euston at rush hour this evening as hundreds of people try to get home in the baking heat.

Trains to Liverpool Lime Street, Manchester Piccadilly, Crewe, Northampton and Bletchley are among the services cancelled due to the hot weather, while others are facing long delays.

Several platforms are closed and people are using handheld fans to try and cool down, while others are sitting on the floor clutching bottles of water.

I’m travelling to Stockport on the delayed 16:53 Avanti West Coast train, which has just departed.

People in front of me were running to try and get a seat on the train.

Thankfully, I’ve found one and the air conditioning is working, but those sitting in coach D are not so lucky.

Commuters are facing widespread transport disruptions due to the hot weather. People are being advised to check their routes before travelling. Here's a list of what's affected:

• In London, severe delays are reported on some Tube lines, including: Victoria Line, Northern Line, Lioness Line and parts of the Bakerloo, Central and District Lines
• The M25 in Kent and Surrey is closed after two vehicles were involved in a serious crash
• Transport for Wales has cancelled services across Wales due to extreme heat and a shortage of trains. The rail operator says some routes will remain out of action until the end of the day
• London North Eastern Railway has told customers to not travel unless it's "absolutely necessary. Disruptions have also been reported by a number of train operators

A major rescue operation is under way after a 15-year-old boy went missing after swimming at a nature reserve.

Emergency services have been attending the scene at Testwood Lakes, near Totton, Hampshire, after the teenager was reported missing at 13:35 BST.

Hampshire Police says it has deployed marine units to aid in the search, with people advised to avoid the area.

The National Police Air Service, South Central Ambulance Service, and Hampshire and Isle of Wight Fire Service have also been sent to the scene.

The June heat record keeps getting pushed higher. The maximum recorded now is a provisional 36.1C in Gosport, Hampshire.

Esme Stallard
Senior climate and science reporter

Image source, Just Farms/Ceri Squire

For those whose livelihoods are dependent on the weather conditions, these repeated heatwaves throw up challenges.

Ceri Squire, a sheep and cattle farmer in Bridgend, says: "The unusual weather means that the seasons, as my in-laws used to farm by, are no longer consistent periods of months. We have to be flexible."

She says that she is having to spray her sheep down regularly to prevent blowflies taking hold and laying eggs in the wool.

Ceri adds: "This week we were planning to take livestock to a local livestock market, but we are legally not allowed to transport animals in temperatures over 30 degrees unless we have a temperature controlled vehicle for them."

For many smaller family-run farms, they are too expensive to have.

This week the National Farmers' Union urged the government to do more to tackle the "stark" impacts of climate change, saying "fields that produce wheat for the nation’s bread can be underwater one year, then parched and cracking the next".

Alex Meakin

The Hurst School in Berkshire is one of many across the county that have closed early today to shield pupils from the warm weather.

A little earlier, headteacher Jayne McLaren told us: “The first most and important thing to me is always the wellbeing of my staff and students.

"The temperatures in some of the class rooms are in the high thirties now and we haven’t got the highest temperatures yet.

“We’ve had many trips to the medical centre. We have children that are suffering with heat exhaustion. It is difficult for us to keep them safe here.”

She said that she hoped things are "back to normal" next week, adding: "The temperature looks like it's coming down to the early 20s which, compared to now, is tolerable."

Image source, Getty Images

BBC Radio 4's Woman's Hour has been speaking to GP Dr Amir Khan on the ways women are impacted differently by extreme heat. He says:

• In the second half of the menstrual cycle, progesterone levels rise, which can raise core body temperature by about half a degree
• During peri-menopause and menopause, oestrogen fluctuations affect the brain so the body can't regulate temperature as well
• Women sweat less than men so the body's evaporation system "doesn't work as efficiently", Dr Khan said

Tips to keep cool include:

• Putting pyjamas in a sealed plastic bag and leaving them in the freezer overnight
• Doing this with a pillowcase if you don't wear pyjamas
• Filling a hot water bottle with cold water and bringing it to bed

Matt Taylor
BBC Weather

Much like you and me picking up bits of our personality from our parents and the friends we’ve met along the way through our lives, weather systems pick up some of their characteristics from where they originated and the environment they have travelled over to get to us.

While we have seen the air heat up rapidly under a large area area of high pressure or "heat dome" sitting over western Europe this past week, one of the most punishing aspects of this heatwave, the humidity, is down to where the the air in it began its story.

Tracking the movement of the atmosphere backwards we can tell that a lot of the air we are breathing now actually originated in the warm and humid mid-Atlantic.

It picked up more moisture as it crossed over the sea and then ended up trapped, circulating around the high pressure system that’s with us now.

It’s that moisture that has increased humidity levels and along with the heat made days and nights so brutal. By contrast, when we had the record-breaking heat in 2022, the air actually originated in West Africa, travelling up via Iberia to us and was therefore much drier.

And the temperature continues to rise - the provisional June record now stands at 36C, which was recorded in Wisley, Surrey.

Ben Rich
Lead Weather Presenter

When a new record temperature is reached, it is almost always described as “provisional”, like today's new June record of 35.7C.

This is because the Met Office - along with national weather services around the world - has a responsibility to make sure weather and climate records are accurate and consistent, meeting internationally-agreed standards.

Once a provisional temperature is set, checks will be carried out to make sure the measuring equipment is properly calibrated and that conditions around the site at the time of the observation didn’t have an impact on the readings.

For instance, a record could be discounted because temporary buildings were erected close to the measuring site or even because the grass or plants close to the weather station were not properly maintained.

In 2022, a temperature of 35.1C that was recorded at Floors Castle in the Scottish Borders – and provisionally thought to be a new record for Scotland – was discounted because the site didn’t meet Met Office standards.

This quality control process can take days or weeks, and a record will remain provisional until those checks are completed.

Image source, EPA/Shutterstock

Climate change has led to more frequent and intense heatwaves, says the Met Office's chief scientist.

Professor Stephen Belcher says human-induced climate change has made events like this "more likely and more intense".

"To see temperatures like this in the UK in June is sobering," he adds.

Met Office projections indicate hot spells will become more frequent in the future, particularly over the south-east of the UK.

Temperatures have soared to 35.7C in Charlwood, Surrey, surpassing the UK's previous June temperature record from 1976 of 35.6C.

BBC Wales News

Transport for Wales (TfW) has cancelled services across Wales due to extreme heat and a shortage of trains.

Routes affected are between Manchester and Cardiff, Coryton and Penarth, Ebbw Vale and Cardiff, Bridgend and Maesteg, Chester and Wrexham, Llandudno Junction and Blaenau Ffestiniog, and Pontypridd and Cardiff Bay.

Most routes will remain cancelled until the end of the day, the operator warns.

Sadaf Maruf
Your Voice news editor

Davide and Vanessa got in touch with BBC Your Voice after the third lift in their 23-storey building broke down this week due to the heat.

The increasing temperatures have taken a toll on the residents of the block in Canary Wharf trying to leave their flats or go home.

Davide says he had to help a woman with a baby climb up to her flat on the 20th floor yesterday, and there are a few elderly people living in the building's 134 flats.

He says residents were told it would be within four hours but they are still waiting and have heard nothing since yesterday,

Vanessa, who rents her flat and has lived in the building for two years, says she had to climb 16 floors with her husky Luna after work using the small airless emergency stairs.

“Its now been 48 hours in this heat. Its just ridiculous, “ she says. “There are always issues with the lifts but never all three out of order.”

The company that manages the building, Sanctuary, has apologised for the issues and says in a statement “our lift contractor is working hard to restore them and we are clear on the urgent need to resolve the problems as soon as possible".

Another temperature update - 35.3C has been recorded in Gosport, Hampshire, and Wisley, Surrey.

We are getting very close to that June record of 35.6C.

Image source, Solentgirl / BBC Weather Watchers

Lola Schroer
BBC News, reporting from Richmond

As temperatures continue to soar, people here in Richmond are finding different ways to stay cool.

Along the riverside, some have been dipping their toes inside, while others have been seeking relief at ice cream vans or retreating to air-conditioned pubs for lunch.

But despite the heat, not everyone is slowing down.

Local fitness instructor Zhivka Slavova taught a yoga class this morning and says turnout was still strong.

She says if people want to stay active during the hot weather it's "important to stay hydrated" and to "prioritise low impact exercise and movement" if you are going to leave the house.

The highest temperatures recorded so far today have been at Bournemouth Airport and Thorney Island in West Sussex, where it was 34.7C as of 14:00.

That tops yesterday, when the maximum temperature in England was 34.6C - and it's going to get hotter still.

Forecasters says the UK’s June temperature record, which stands at 35.6C, could be broken today.