This article is more than 1 year old

This article is more than 1 year old

Large swathes of Britain have experienced storms and lightning strikes as the country braces for what could be its hottest day ever later this week.

Thunderstorms moved into southern and western areas late on Tuesday evening, with the Met Office issuing a yellow severe weather warning for most of England, Wales and Scotland until 9am on Wednesday.

Surrey police posted a video of what it called “a great lightning show” and some Twitter users posted to say they had been woken by the thunderstorms.

North Wales was the wettest area overnight, getting 15mm of rain in one hour. By Wednesday morning, much of the country was already experiencing temperatures far above normal for this time of year.

“Quite a lot of places are back up to 23 or 24 degrees already (at 5am),” said Emma Smith, a Met Office meteorologist. “It’s normally 13 or 14 degrees at this time of year, so that’s 10 degrees above average.”

The extreme heat comes after temperatures across England exceeded 30C (86F) on Tuesday, with forecasters predicting even hotter temperatures on Wednesday.

“It will get to 35 degrees on Wednesday, with a small chance it will get to 36C,” said Smith.

The highest overnight average temperature ever seen in the UK was 23.3C (73.94F) in July 1948. Smith said there was a possibility this would be beaten on Thursday night into Friday.

Temperatures in London were expected to reach 38C (100.4F) on Thursday, which would pass the record for a day in July – 36.7C (98.1F) – recorded at Heathrow in 2015.

The Met Office said there was a 40% chance the UK temperature record of 38.5C (101.3F), which was recorded in Faversham, Kent, in August 2003, would be exceeded.

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Northern Ireland and western Scotland will be the coolest areas on Thursday, with temperatures in the low 20s.

The train company Southeastern said it would be running a “significantly reduced service” on Thursday due to speed restrictions announced by Network Rail. Southeastern operates trains in south-east London and Kent and also serves parts of East Sussex.

Dr Sam Hampton, a post-doctoral research associate at the Environmental Change Institute, University of Oxford, advised people to wear “lighter, loose-fitting clothing before cranking up the air conditioner”, adding: “If necessary, air-conditioners should only be run when all the windows are closed.”

In London, police were searching for three people who have gone missing in the Thames. The Metropolitan police said a swimmer went missing at Shadwell Basin on Tuesday evening, a second at Waterloo Bridge and a third near Kingston High Street.