Storms have caused further disruption in parts of the UK after recent high temperatures and lightning strikes.
The roof came off a house struck by lightning in Chelmsford
Heathrow Airport has asked airlines to cancel one in five flights between 16:00 and 18:00 BST. Airlines say other London flights could be delayed.
The roof of a house in Chelmsford collapsed after being struck by lightning overnight. No-one was hurt.
There are amber weather warnings for rain
in place for most of England and Wales. There are also flood alerts
Heathrow said there was a strong likelihood of thunderstorms, lightning strikes and hail, which can significantly reduce capacity for take-offs and landing.
About 20 flights will be cancelled and passengers have been advised to check whether their flight will be operating before travelling to the airport.
Manchester Airport said an electrical surge caused by thunderstorms had caused some delays.
General duty manager Gary Brown said: "It impacted on some lifts and baggage systems but most systems are now back up and running. We'll wait to see what happens this afternoon when we're expecting thunder."
Gloucester was among the cities to see lightning on Friday - more is expected in other areas