The Met Office has issued an 18-hour yellow thunderstorm warning for Monday, which runs from 6am until 11.59pm.
In their warning, forecasters say: "While some places stay dry, thunderstorms are likely to develop during Monday, bringing locally heavy rain and possible disruption.
The warning covers vast swathes of the UK, including all of Wales, the Black Country and wider West Midlands, wider West Midlands, East Midlands, South West, North West and North East of England, as well as all of Scotland and Northern Ireland. Only London, the South East, East Anglia and parts of the east coast of England have escaped the warning.
Storms are expected to develop across parts of England and Wales by late morning and into the afternoon before easing from the east later on.
"Very locally 20-30 mm of rain is possible in an hour, and up to around 50 mm in three to six hours. Hail and frequent lightning are also possible," forecasters warn.
The Met Office also warns of a "small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds".
It also tells people to expect some cancellations to train and bus services in places where flooding or lightning strikes occur, while spray and sudden flooding could lead to difficult driving conditions and some road closures.
There is a slight chance that power cuts could occur and other services to some homes and businesses could be lost.
Temperatures in some Shropshire towns are due to hit 33C today and tomorrow, and remain above 30C until Sunday, the final day of the amber extreme heat warning.
Met Office forecasts predict that temperatures will drop to 25-27C on Monday, during the thunderstorm warning, before going down further to around 20C from Tuesday onwards.