By Andre Rhoden-Paul & Katy Austin, transport correspondent
BBC News
The Met Office has issued an amber thunderstorm warning, as parts of the UK are set to be battered by heavy rain, lightning, hail and strong winds.
The warning, in place in central England until 19:00, means flooding and travel disruption is likely.
Three lower-level yellow warnings cover other parts of England, Scotland and the west of Northern Ireland.
Thousands of people had flights axed due to storms on Sunday, with knock-on cancellations on Monday.
Meanwhile, warm temperatures are due to remain throughout the week.
Thunderstorms and torrential downpours with the risk of lightning and hail could bring disruption to Wales and parts of England.
Slow-moving thunderstorms are also forecast for the west of Northern Ireland and much of Scotland.
The Met Office warns power cuts and flooding of homes could occur, along with cancellations to trains and bus services. Spray and sudden flooding could also lead to difficult driving conditions and some road closures.
The Environment Agency has issued 14 flood alerts across the Midlands, such is the concern over heavy showers could produce large amounts of surface water.
Gatwick Airport in West Sussex is encouraging passengers to contact their airline for further information due to the thunderstorms expected throughout the day.
Thunderstorms in the south of England on Sunday led to flight cancellations, with knock-on cancellations on Monday due to planes being out of position.
EasyJet axed over 50 flights to and from Gatwick Airport on Sunday, and a similar number on Monday. More than 15,000 easyJet passengers have been affected.
The airline has apologised to customers for the disruption, which they said was “out of their control”.
A spokesperson said: “We are doing all possible to minimise the impact on our customers, providing those on cancelled flights with options to rebook or receive a refund as well as hotel accommodation and meals where required.”
Passengers are not entitled to compensation in this case under UK consumer law as the disruption’s cause is out of the airline’s control, but passengers must be offered new flight options, food and drink, and overnight accommodation, if required.
BA cut six flights to and from Gatwick and around 20 between London’s Heathrow Airport on Sunday, with a few cancellations of Heathrow flights on Monday due to the knock-on effect.
Jo Rhodes, deputy editor of consumer magazine Which? Travel, said: “While EasyJet does not have to pay compensation for these cancellations, it must offer affected passengers the option of a refund or to be rerouted at the earliest opportunity – even if this means booking seats with a rival carrier to ensure minimal delay.
“If delayed for more than two hours, passengers will be entitled to assistance such as free meals or refreshments, and overnight accommodation if required.”
Meanwhile, the Gatwick Express, which runs non-stop trains between the airport and London Victoria railway station, was suspended on Monday due to track repairs.
Monday will remain a very warm day for most but also very wet with potentially “a month’s worth of rain falling”, according to the Met Office.
“Within these areas, we can expect heavy rain, possibly hail, potentially frequent lightning,” meteorologist Grahame Madge said.
“By their nature, [storms] develop quickly and in almost seemingly random areas.”
He suggested people made preparations like charging phones in case there was a flash flood or a power cut.
The forecast comes after a weekend of warm temperatures and heavy rainfall.
Kew Gardens in south-west London recorded 32C on Sunday, with much of UK sporting higher temperatures than Monaco and the French Riviera, where temperatures remained in the low 20s.
The UK Health Security Agency (UKHSA) has also issued an amber alert for hot weather until 0900 BST on Tuesday in the West Midlands, East Midlands, east of England, South East and South West.
It means high temperatures could affect all ages and impact the health service.