Thunderstorms and flash flooding have sparked chaos across Britain this morning with commuters struggling to get to work after trains were cancelled and roads submerged underwater. 

Heavy rain swept across southern England overnight, forcing operators to impose emergency speed restrictions and warning passengers to expect longer journey times.

Forecasters believe this extreme weather is being driven by a powerful ‘heat dome’ settling over western Europe, as the UK braces for a potentially record breaking heatwave. 

Later today June’s longstanding UK record of highs of 35.6C, set in Hampshire in 1976, is expected to be broken.

The UK Health Security Agency has issued a red heat health alert covering London, the South East, South West, East of England, East Midlands and West Midlands from 1am on Wednesday until 11pm on Thursday.

The warning indicates ‘a risk to life for even the healthy population’ and highlights the threat to transport systems, power supplies, water resources and businesses. 

The travel chaos also hit the London Underground this morning, with the Circle line suspended, severe delays on the Hammersmith & City line and parts of the District line shut. 

The Elizabeth line was also hit by severe delays, while services between Heathrow Terminal 4 and Heathrow Terminals 2 & 3 were suspended due to flooding.  

A bolt of lightning behind Stonehenge in Wiltshire on Monday evening

A lightning strike is believed to have caused a house fire in Bristol

Met Office amber weather warning in place for Tuesday for most of Southern England

Amber and red weather warnings in place for Wednesday and Thursday across the UK 

Large parts of the South West were battered by the lightning overnight causing mass power outages.

As hundreds of homes in Shepton Mallet, Glastonbury and Bristol temporarily lost electricity, and a lightning strike is believed to have caused a house fire in Bristol leaving the roof and first floor of the home ablaze.

One neighbour posted said: ‘We are in the next road and the explosion was quite something.

‘We knew something had been hit as soon as it happened and then saw the smoke. I’m so glad no one was injured.’

A fire service spokesperson said: ‘Upon arrival, crews found the house well alight.’

Videos posted on social media showed flames enveloping most of the roof and black smoke billowing into the sky.

London Fire Brigade (LFB) has also said it had responded to around 400 calls overnight, including two house fires believed to be caused by lightning strikes and flooding of homes. 

Rail passengers across the South East faced delays this morning as signalling systems were affected by the severe weather and precautionary speed limits were introduced to protect infrastructure following the downpours.

Southeastern issued an early morning alert to passengers, warning: ‘With ongoing thunderstorms and heavy rain in a number of areas, speed restrictions have been imposed in many places across the network as a precaution. Trains are continuing to run on all routes but your journey may take longer than expected.’ 

The disruption comes at the start of what forecasters say could become one of the most extreme June heatwaves ever recorded in Britain.

Temperatures are expected to surge dramatically today before peaking on Wednesday and Thursday, when parts of England and Wales could approach 40C.

Thousands of rail passengers faced a morning of travel chaos today after overnight thunderstorms and torrential rain triggered signalling problems. Pictured: Lightening strikes in Sheerness, Kent

Parts of the South West were battered by thunderstorms on Monday evening, with lightning strikes, power outages and transport disruption reported across the region. Pictured: Sheerness, Kent

The Met Office has issued a rare red warning for extreme heat covering a vast area stretching from London to Swansea and from Somerset to Birmingham, warning of ‘severe and significant impacts’ and even danger to life.

A woman bather has already tragically died after falling ill on Bournemouth beach during the heatwave.

The woman, who was aged in her 60s, was believed to have been in the sea with a child when she suffered a medical episode shortly after 2pm yesterday.

She was recovered to the sand by members and a beach hut owner called 999.

Ambulance crews rushed to the scene at Southbourne beach and paramedics carried out CPR on her for some time while a screen was put up around them.

A spokesperson for Dorset Police said: ‘At 2.21pm on Monday we were called to assist with a medical emergency at Southbourne promenade to clear an area to enable emergency services to attend safely.

‘Sadly, a short time later a woman was pronounced dead at the scene. Her next of kin is aware and the coroner has been notified. The death is not being treated as suspicious.’

Network Rail has urged passengers to think carefully before travelling as soaring temperatures threaten further disruption to services.

In an warning, the rail operator said passengers travelling to, from or within areas covered by the red weather warning should only make journeys if they are absolutely essential on Wednesday and Thursday.

Rail services will continue to run, but trains will be forced to operate at reduced speeds because extreme heat can cause rails to expand and overhead power lines to sag, increasing the risk of delays, cancellations and last-minute timetable changes.

There will also be no rail replacement bus services during the peak of the heatwave.

One commuters woke to major disruption after heavy rain swept across southern England overnight

The extreme conditions have already forced dozens of schools to alter plans, with some closing entirely and others introducing early finishes

Jake Kelly, deputy chief executive of Network Rail, said: ‘Extreme heat can have a significant impact on the railway, so safety must come first.

‘We’re asking passengers to check before travelling on Tuesday, and only travel if absolutely essential on Wednesday and Thursday if they are going to, from or within the red warning zone as temperatures are expected to peak.

‘If you do need to travel in this area or outside of it where it will still be hot, please plan ahead, allow extra time and take necessary precautions, such as carrying water, to stay safe. We thank passengers for their patience and understanding during this period.’

Transport for London has also warned of possible disruption across rail and Tube services as track temperatures rise.

Claire Mann, TfL’s chief operating officer, said: ‘Customers should be aware that, given the very high temperatures that are forecast, we are likely to see some disruption to rail and Tube services – with rail temperatures likely to lead to temporary speed restrictions and therefore reduced services in some cases.

‘This will vary by line, with some services that share parts of the overground rail network – like the Overground and the Elizabeth line – likely to be more affected.’

The extreme conditions have already forced dozens of schools to alter plans, with some closing entirely and others introducing early finishes.

The Buckingham School in Buckinghamshire will shut on Wednesday and Thursday, while schools across Wiltshire, London, Berkshire and Surrey have announced closures or reduced hours.

National Association of Head Teachers general secretary Paul Whiteman said: ‘While there is no legal ‘upper limit’ for temperature in schools, (school leaders) will certainly be doing all they can to mitigate the effects of such high temperatures.’

Road users are also being warned to expect disruption as temperatures rise.

The AA said gritters could be deployed to spread stone chippings on roads at risk of softening in the heat, while RAC road safety spokesperson Rod Dennis urged motorists without effective air conditioning to avoid non-essential journeys in areas covered by the red warning.