The UK was struck by lightning between 15,000 and 20,000 times as the "mother of all thunderstorms" rolled across southern England overnight, meteorologists said.
There were cancellations and delays after a thunderstorm and lightning strikes overnight.
The London Fire Brigade said it had taken more than 500 weather-related calls as the warm and humid bank holiday weather broke down into an "utterly intense" storm.
In Warwickshire, the fire service said five properties were struck by lightning in the early hours of Sunday, while in Dawlish, Devon, a telephone box burst into flames after a BT pole was hit on Saturday evening.
Western Power Distribution said nearly 1,000 properties had been left without power across the Midlands, with the majority of outages down to lightning.
A cluster of 17 flood alerts has been issued for parts of the Thames Valley, while West Midlands and Bedfordshire fire services warned motorists of the risks of driving on flood-hit roads.
Met Office meteorologist Charlie Powell said information suggested there were "somewhere between 15,000 and 20,000 strikes across the UK during the overnight period".
He explained: "Temperatures overnight did not fall much below 15 or 16 degrees, for the end of May that's a pretty hot and humid night so everything was primed.
"We had some storms coming in from northern France and some building up in the Channel and they sort of spread out and have been working their way in.
"It looks like there just one huge area of thundery showers that worked across London just before midnight."
The LFB said it had taken 505 weather-related calls overnight, although the majority were down to flooding and no fires were reported to have been started by lighting strikes.
Torrential rain at Kew Gardens, in south-west London, saw more than half an inch of rain fall in an hour.
A Met Office warning of heavy thunderstorms is in place until 6am on Monday, covering much of England and all of Wales.
As it played out in dramatic fashion, skies exploded with light and sound over the capital and across southern England.
BBC weatherman Tomasz Schafernaker tweeted: "Mother of all #thunderstorms now over London. Oh boy! This UTTERLY INSANE. I've never seen a storm with such frequent lightning in my life I don't think. Mostly sheet lightning and not too loud but flashes are spectacular."
James Brewin captured the moment Big Ben and Westminster were illuminated by a flash of lightning, describing it as "London in daylight at midnight for a split second".
Photographer and journalist Andrew Lanxon Hoyle shared an image of the Suleymaniye Mosque in Dalston, east London, lit from behind by a brilliant fork of lightning, tweeting: "The lightning storm over London right now is utterly INTENSE."
Pamelasaurusrex shared a photo on Instagram of two people running for shelter outside King's Cross Station as a lightning bolt arced across the sky over nearby St Pancras.
Samuel Wilkinson captured the split-second lightning shot toward the earth with The Shard skyscraper below, while the RNLI at Tower Bridge shared a photo of the view over the South Bank as the sky lit up.
The fuelling system at Stansted was repaired on Sunday morning, but passengers were warned to check before travelling.
The airport said in a statement: "Due to an earlier lightning strike, the aircraft fuelling system was unavailable for a period this morning.
"Engineers have been on site and have now restored the system, however flights may still be subject to diversion, delay or cancellation.
"We apologise for the inconvenience and advise all passengers to check with their airlines for their latest flight updates."
Ryanair could not say how many of its flights had been affected, and said customers can get a full refund or free transfer.
"A number of flights have regrettably been cancelled at Stansted Airport this morning due to an earlier airport fuelling system failure, caused by a lightning strike," a spokesman said.
"All affected customers are being contacted and advised of their options of a full refund, a free transfer on to the next available flight or a free transfer on to an alternative routing.
"We apologise to all customers affected by these disruptions, which are entirely beyond our control."