It is likely to reach 30C in Wales on Thursday, so where can you go to keep cool?

British Transport Police say they are assisting train firms and passengers amid widespread disruption.

You can check the status of services here, external.

A passenger on board a train from London Euston to Manchester Piccadilly tweeted this photograph of a packed train, which she said was awaiting evacuation.

Network bosses have cancelled trains because of concerns the hot weather will buckle tracks.

A "number of heat-related incidents" have caused delays and cancellations across the country today, says Nick King, network services director at Network Rail.

He apologised to passengers experiencing uncomfortable conditions and inconvenience.

"Our teams are working flat out to fix the issues as quickly as possible and get people on the move," he said.

He advised people to check with their train operators or visit the National Rail Enquiries, external website before they travel.

A passenger says he was stuck on a train for almost three and a half hours after it stopped just 800ft (243m) away from the station.

James Fenn boarded the 13:20 train from Euston to get home to Milton Keynes, but the train ground to a halt as part of the major disruption affecting large swathes of the rail network.

He said a rescue train arrived "quite quickly" but it took almost two hours for everybody to transfer to it, which included climbing down ladders.

Mr Fenn said: "The rescue train was already quite busy so everyone was just dripping with sweat.

"I’m still at Euston. Everything has been disrupted so I don’t know how I’ll get home to Milton Keynes."

Bottled water was being delivered to vulnerable people and bowsers were being put in place.

Image source, Dan Kirkby

Passengers on the line to Hastings from London have complained of hot and overcrowded trains.

Southeasterm blamed a combination of speed restrictions imposed on the network due to the danger of rails buckling in the heat, and a fault on a train at Tunbridge Wells.

The train operator said trains were beginning to move again on the line from London to the Sussex coast.

Dan Kirkby tweeted, external: "Inhuman overcrowding on the Hastings line tonight, stifling heat, huge numbers of cancellations."

This week's "dangerous heatwave" should be a "stark warning" to new Prime Minister Boris Johnson about the need to tackle the climate emergency, according to Friends of the Earth.

The environmental group is "urging" Mr Johnson (pictured below) to put tackling climate change "at the heart of his new government", especially moving away from fossil fuels into more renewable energy sources.

Image source, Getty Images

Friends of the Earth chief executive Craig Bennett said: “Developing the UK’s vast renewable power potential, insulating our heat-leaking homes and investing in modern, carbon-free transport systems would slash emissions, create thousands of new jobs and put the UK at the forefront of building a cleaner, safer future."

Nick Smith
BBC News Online

All East Midlands Trains services running between Nottingham and London have been cancelled, the operator has confirmed.

The cancellations have been caused by damage to overhead wires at Belsize tunnel, near West Hampstead.

East Midlands Trains said the damage was "almost certainly heat related".

Major disruption is expected to continue until 22:00.

Image source, PA

National Rail is reporting major disruption on a number of train routes due in large part to the heat.

These include:

• At Peterborough until at least 18:00, external
• Between Luton and London St Pancras International until 22:00, external
• West Anglia services to and from London Liverpool Street until the end of the day, external
• On the West Coast Line and in the Birmingham area until the end of the day, external

Other services affected by issues, external include c2c, Chiltern Railways, CrossCountry, East Midlands Trains, Gatwick Express, Grand Central, Great Northern, Great Western Railway, Greater Anglia, Hull Trains, LNER, London Northwestern Railwasy, London Overground, Southern, Stansted Express, TfL Rail, Thameslink, Transpennine Express and Virgin Trains.

Some people queuing at Peterborough Lido needed medical help as nearby Cambridge broke heat records.

Emily Anderson
Reporter, BBC East Midlands Today

This is how people in landlocked Nottingham enjoy the sunshine - on the beach in the city's market square.

Many have travelled from other parts of the East Midlands and some told me they make the trip every year.

Another family told me it’s nice to be able to go to the beach and not to travel out of Nottingham.

And on such a hot today, myself and cameraman John Ross couldn’t resist an ice cream to cool down!

Dementia UK has issued advice to help people with the condition cope, external with the heat.

A person with dementia may not be able to explain that they’re dehydrated or feeling unwell because of the heat, the charity said.

They could also forget to wear loose, cool clothing as well as hats and sunglasses.

Image source, Dementia UK

Dementia UK CEO Dr Hilda Hayo said: "Ensure that any cups or glasses are nearest to the hand they write with and they can easily see them.

"Try not to include pieces of fruit within the water as this can sometimes be confusing and off-putting for a person with dementia. If the person prefers to drink fruit squashes add this to the water as this can make it more appealing for the person and easier for them to see."

Amy Woodfield
BBC News

East Midlands Trains are warning passengers they're not expecting the railway line near Luton to reopen for the duration of the day.

Image source, East Midlands Trains

Damage to the overhead electric wires at Belsize tunnel has halted all services in and out of London.

The operator says trains that have already started their journey will now terminate.

A reduced train service had already been in force because of the weather.

This was the scene a short time ago at Flamborough Head in East Yorkshire as the hot weather continues.

Image source, Joy Medina O'Brien

Joy Medina O'Brien, from Harrogate, took the photo showing the distinctive coastline as temperatures there top out at 23C (73F).

In case you hadn't noticed, the country is in the middle of a heatwave, with temperatures in other parts of Yorkshire hitting 34C (93F).

There are hailstones as big as 20ps falling in Liverpool.

Could this day be anymore hot and cold with us?

Railway companies are advising passengers not to start new journeys as high temperatures are causing chaos on the network.

Several lines around London have been beset by problems causing delays and cancellations with major disruption also on the West Coast Line and in the Birmingham area.

You can check the latest service information here, external.

If you do have to travel, companies are urging passengers to carry a bottle of water and be prepared for delays.

The temperature in Cambridge has reached 38.1C, making today only the second time in history 100F has been recorded in the UK.

Amy Woodfield
BBC News

Problems disrupting the railway line has forced East Midlands Trains to tell passengers not to attempt to travel on the Sheffield / Nottingham and London St Pancras International route.

A high track temperature speed restriction - caused by the hot weather - has meant an amended timetable has been running all day.

There's now an additional problem with the overhead electric wires between Luton and London St Pancras International resulting in all lines being blocked.

There are also major problems with the Nottingham tram service due to the hot weather.

NET is reporting delays to all services but says: "We are working hard to make sure our trams are cool enough before going back into service".