Great Western Railway says some trains are delayed or cancelled due to the hot weather.

Stations in the Thames Valley are affected, and some trains between Reading and London Paddington will be cancelled.

The train operator says "track temperatures are forecast to reach levels requiring speed restrictions. Extreme heat can cause rails to expand and buckle, so when temperatures reach certain thresholds, trains must run more slowly to keep services safe."

National Rail says there is disruption on the routes from Coryton and Penarth in south Wales, and between Pontypridd and Cardiff Bay, and people can use their tickets on the bus routes instead.

Vanessa Clarke
Education reporter

The government doesn’t normally advise schools to close – it says most of the time it can be managed safely and keeping children in school is important.

But it does expect schools to adapt to keep children safe and comfortable.

Some parents, like me, will already have had a message from their schools saying uniform rules are being relaxed, PE kits are allowed and sunscreen and sun hats are needed.

Head teachers in older school buildings, which are sometimes harder to keep cool, will have been up early opening up doors and windows to keep air moving.

Advice from the UK Health Security Agency says schools may have to close their windows later in the day if it becomes hotter outside than inside, and fans shouldn’t be used if temperatures go above 35°C.

Lessons may be moved to cooler areas of the school and hot meals may be switched for cooler options.

And schools could even look at changing start and finish times to avoid the worst of the heat – so things could look a little different this week.

Bea Swallow
BBC News, West of England

A number of schools across the West region have confirmed they will close early, citing concerns over staff and pupils spending prolonged periods inside stuffy classrooms.

In Wiltshire, Kingdown School, Clarendon Academy, Pewsey Vale School and Dilton Marsh Primary are among those who say lessons will finish at 12:30 BST.

Kingsholm Primary in Gloucester will close its doors at 13:30 BST every day until Thursday, and it has advised pupils they are welcome to wear their PE kits to class.

Justin Rowlatt
Climate editor

We tend to experience heatwaves as: a sweaty commute, a sleepless night, a warning to stay indoors. But the bigger story is even more unsettling.

Human civilisation has developed during roughly 12,000 years of unusual climate stability - a narrow band of conditions in which farming, trade, cities and all of modern life became possible.

Now, over the course of a few decades, we are pushing that system into new territory.

One broken temperature record does not prove climate change. But records falling repeatedly, across continents and seasons, show the dice are being loaded towards extremes.

That is why this heat matters.

Image source, Met Office

A red warning is the most severe level of alert which indicates dangerous weather is expected with a high likelihood of risk to life.

It could also lead to failures of critical national infrastructure, such as power outages or roads and rail lines being closed.

In situations where a red warning is issued, the Met Office advises people to avoid travelling where possible and to follow the advice of the emergency services and local authorities.

The first ever red heat warning was issued in July 2022, although the extreme heat warning system was only introduced in 2021.

Simon King
Lead weather presenter, BBC Weather

The rare red extreme heat warning issued by the Met Office covers parts of southern England, as well as the Midlands and southern Wales.

It will come into effect at 09:00 BST on Wednesday until until 21:00 BST on Thursday.

Red warnings indicate that dangerous weather is expected with a high likelihood of risk to life.

The Met Office is also warning of substantial disruption to travel, energy supplies and possibly widespread damage to property and infrastructure.

The Met Office has issued a rare red warning for 09:00 on Wednesday to 21:00 Thursday for parts of England and Wales.

This means the heat is likely to bring impacts to health and could be a danger to life, but also a risk to infrastructure such as power supplies and transport.

Temperatures will increase significantly in the next few days with the potential for 38 or 39C by Wednesday and Thursday.

Amber warnings are also in force across a wider area from now until Thursday.

Image source, Met Office

The Met Office has issued a red weather warning for parts of England and Wales on Wednesday and Thursday.

We'll have more on this in our next post.

Helen Willetts
BBC Weather

This potentially record breaking and dangerous heatwave is not limited to here in the UK, it's affecting much of western Europe.

The heat is building due to a combination of factors:

Firstly there is a strong high pressure sitting across Europe which acts like a lid trapping the heat in the lowest layers of our atmosphere.

Then at this time of year we have a positive energy balance, simply we get more heat in from the sun than we lose.

As a result of the high pressure position we have a southerly drift over the UK, so as well building our own heat we are importing heat from Europe - where it's also highly likely to be record breaking.

Despite recent rain, the ground is now pretty dry which means all of the sun's heat goes into raising the ground and air temperature and not evaporating moisture.

Red warnings are in force for extreme heat across much of France, and some French schools have closed for the day.

Red warning are also peppered across Spain and Germany today with Luxembourg joining tomorrow, and more extensive amber warnings.

Here is a forecast for the next few days in Madrid, Bordeaux, Paris and London:

There are a number of obvious and not-so-obvious tricks to keep yourself and your pets cool during the hot weather. Here we've rounded together tips you can follow as temperatures soar this week.

Image source, EPA/Shutterstock

As we've been reporting, the heat is spreading from continental Europe where an extremely intense hot spell has developed.

Temperatures in parts of western France could climb to 43 or 44C (109-111F) over the next few days.

Red heatwave alerts have been issued for about half of the country for Monday, with nearly 850 schools closed and 1,500 more allowing pupils to leave early.

Paris is likely to reach 40C (104F) which would be unprecedented for June.

Helen Willetts
BBC Weather

On Sunday, an official heatwave was declared at Writtle, near Chelmsford, Essex.

It has now seen three consecutive days above the heatwave threshold of 27C, and many others will join today or tomorrow.

This is expected to be a record breaking and potentially dangerous heatwave and while hot weather is not uncommon during the UK summer, the current amber warning and potential escalation to red highlights the severity, duration and widespread nature of this event.

On top of daytime heat, overnight temperatures are forecast to remain unusually high, with some urban areas struggling to fall below 20 or 21C, resulting in so-called tropical nights.

This combination of hot days and very warm nights gives no chance for the body to cool down, some places are likely to have a run of three or four successive days and nights in this heat, so it will soon become exhausting, especially, but not only for the vulnerable.

This heatwave is likely to differ from that in 2022 as the humidity is higher, making it even more uncomfortable.

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Image source, EPA

Temperatures could soar to 38C (100F) in parts of England this week as the Met Office has issued a four-day amber warning for extreme heat.

The warning came into effect at 01:00 BST on Monday and will remain in place until 23:59 BST on Thursday.

Large swathes of England and Wales are covered by the warning, which will extend to more northerly areas on Wednesday and Thursday.

The warning means population-wide impacts are likely, including serious health risks, disruption to daily routines and increased pressure on infrastructure.

The heat is spreading from continental Europe where an extremely intense hot spell has developed.

In parts of western France the mercury is expected to climb to 43 or 44C over the next few days, while temperatures in Belgium are expected to be "the hottest ever recorded".

We'll bring you the latest forecasts, developments and top tips on how to stay cool during the warm weather on this page - stay with us.