Temperatures continue to soar around the UK as forecasters anticipate what could be the hottest day on record.
The Met Office says southern and eastern England could experiece a record-breaking 39C (102.2F) on Thursday, beating the all-time high of 38.5C recorded in 2003.
It said there was a 60% chance that the record would be broken.
Meanwhile, a body has been found after three people went missing in different parts of the River Thames on Tuesday.
Police believe it is a 23-year-old man who vanished while swimming with friends near Shadwell Basin in Wapping, east London.
Forecasters say temperatures in some parts of the country could reach 36C (97F) later on Wednesday. Northern Ireland and western Scotland are expected to be the coolest areas with temperatures in the low 20s.
The Met Office has also issued a yellow weather warning for thunderstorms which are expected to affect most of England and southern Scotland from 16:00 on Thursday and last into the early hours of Friday morning.
Thunderstorms swept across much of the UK on Tuesday night, with 48,000 lightning strikes reported.
The NHS has tweeted advice for dealing with the unusually hot temperatures and said: “Try to avoid spending extended periods in the sun this week. Also, be aware that vulnerable people are at increased risk of health issues.”
The London Ambulance service added: “If catching a train or the Tube in this hot weather make sure you carry a bottle of water and step off the train at the next station if you feel unwell.”
Councils have called on the public to check on family and friends, warning that the elderly and those with heart and respiratory problems were most at risk from the hot weather.
Network Rail has said speed restrictions may need to be introduced on Thursday “at vulnerable locations” to “reduce the likelihood of buckling”.
It advised passengers to check their trains before they travel.
Rail operator Southeastern has said it will run a “significantly reduced service” on Thursday due to the speed restrictions.
The Rail Delivery Group, which represents the industry, advised passengers in London and the South East to consider changing their travel plans on Thursday because of the expected heat.
Meanwhile, passengers on a Eurostar train travelling from Brussels to London were stranded in 38C on Wednesday morning, after their train broke down due to an overhead power supply problem.
The train was evacuated and passengers were given bottles of water while they waited for another train to collect them.
Eurostar advised people not to travel on its Brussels route because the power issue was causing “significant delays”, as well as some cancellations.
Belgium’s record temperature was broken on Wednesday as temperatures soared in Western Europe.
The town of Kleine Brogel in Limburg province hit 38.9C (102F), beating the previous record set in 1947.
The French city of Bordeaux also hit its highest temperature since records began, registering 41.2C (106.1F).
Lightning ‘like a gunshot’
People in parts of England and Wales are inspecting damage to their property following the fierce thunderstorms on Tuesday night.
One house in north Wales caught fire after being hit by lightning.
Megan Zahra, from Wrexham, said a lightning strike sounded “like a gunshot” when it set her bedroom roof on fire.
She woke up but thought it was a noise from outside and did not know the roof was on fire until her stepfather arrived to get her out.
Ms Zahra, 23, told BBC Wales: “I heard this big… it was like a gunshot or an explosion. I thought it was just outside here so I checked the window and didn’t see anything so I got back into bed.
“About 15 minutes later my stepdad was outside going, you need to get out, it’s on fire.”
In Lancashire, two lightning spotters had to be rescued from a beach by police when their car got stuck amid a “spectacular” storm.
Lancashire Road Police said the pair were parked on sand off Carr Lane in Middleton, near Morecambe, when the car became embedded.
Officers helped release them before the tide came in and have urged people not to try and drive on to beaches.