Thunderstorms are moving across parts of the UK, after some areas saw the longest stretch of high temperatures since the 1960s.
The severe weather caused flash floods in parts of southern England on Thursday, bringing travel disruption.
The Met Office has issued yellow thunderstorm warnings for the next five days in much of England and Wales, with flooding, lightning and hail expected.
It comes after torrential rain and lightning lashed parts of Scotland.
Part of the M25 motorway in Surrey was closed because of flash flooding, while in Kent 19 people have been evacuated from a train which became stuck after a landslide.
The Met Office has warned that while some areas could stay dry, others could see as much as 40mm of rain falling in less than an hour amid severe thunderstorms.
There were thundery showers across southern England on Thursday afternoon, including the counties between Devon and Kent.
BBC Weather said about 12,000 lightning strikes were detected across parts of southern Britain in the hours leading up to 18:00 BST.
A wooden pavilion caught fire after a suspected lightning strike in the village of Barton Stacey in Hampshire, with eyewitness Donna Stokes saying there was a "horrendously loud bang of thunder".
In Devon, homes were flooded following a collection of thunderstorms across south-west England on Thursday.
Devon and Somerset Fire and Rescue Service said on Twitter it had received numerous calls relating to properties in Devon, with some residents reporting up to 18 inches of water inside their homes.
The Environment Agency has issued flood alerts for certain areas in England and Scotland, which are separate from the weather warnings issued by the Met Office.
Thursday's heavy downpours also sparked travel disruption on rail and roads in southern England.
There are closures in both directions on the M25 between junctions seven and eight near Reigate in Surrey due to flooding, according to Highways England.
Motorists have been urged to allow additional time for journeys, as the disruption has caused delays of one hour and about seven miles of congestion.
One motorist reported "biblical" rain and hail on the M25 near junction seven, as he shared a video of the flooding.
Hammersmith Bridge in west London has been closed to pedestrians after cracks in the structure worsened during the recent hot weather.
Meanwhile, British Transport Police rescued 19 people from a train which came to a stop between West Malling and Borough Green on Thursday.
Train operator Southeastern said the line between Otford and Maidstone East was expected to remain closed.
A tweet by Network Rail Kent and Sussex said teams would be working overnight to clear mud which was washed onto the railway by torrential rain in the area.
Network Rail warned of continuing disruption across the entire Southern and Thameslink networks due to severe weather conditions.
It said reports of a landslip in the Merstham area in Surrey had closed the railway line via Redhill between East Croydon and Gatwick. Flooding had also shut the railway between Tattenham Corner in Surrey and Coulsdon Town in Croydon.
Forecasters have warned severe thunderstorms could continue to bring flooding and disruption into next week.
Met Office meteorologist Matthew Box said there was a risk of thunderstorms "right through to the start of next week, and maybe even beyond that".
But he added that temperatures were cooler on Thursday, following days of scorching weather in parts of the UK.
A high of 29.6C (85.3F) was recorded in the village of Frittenden in Kent, Mr Box said.
It comes after temperatures surpassed 34C in central London for the sixth day in a row on Wednesday - the first time that has happened since at least 1961.
Skies across the UK were lit up by lightning as thunderstorms hit on Wednesday evening, following the week of hot weather.
Lightning struck a house in Wrexham, blowing out power sockets and setting fire to a curtain.
Fire crews were also called to deal with flooding incidents around Wrexham, as well as other parts of Wales including Denbighshire and Powys.
Several other places have recorded heavy downpours over the past 24 hours, such as Gnosall, West Midlands, which recorded 103.8mm of rain - over a month's worth - in one night, according to BBC Weather.
On Wednesday, three people died after a passenger train derailed near Stonehaven in Aberdeenshire. It is thought the train hit a landslide after heavy rain and thunderstorms.
Scotland's Transport Secretary Michael Matheson said extreme weather "had an impact" on the accident.
A major incident was also declared in Fife. The Scottish Fire and Rescue Service said it received more than 1,000 emergency calls on Tuesday night due to the severe weather.
The Environment Agency said 10 properties in Lancashire were also affected by flooding following storms.
Meanwhile, Devon and Cornwall Police warned the south west of England is "full to capacity", leading to "unprecedented demand" for 999 services.
The force said it saw an increase in anti-social behaviour and public order offences on Saturday and Sunday.
Assistant Chief Constable Jim Colwell said the weekend's events, spurred on by the hot weather, had forced officers to attend a "plethora of different incidents".
And in Sussex, more homeowners had water supplies cut off or restricted on Wednesday. At least 300 householders had already been without tap water since Friday.
Steve Andrews, head of central operations for South East Water, said more than 150 million litres of extra water were being pumped into the network as the UK heatwave continues.