The Met Office has issued a yellow ‘be aware’ warning and said up to 70mm of rain could fall in just a few hours.
It said: “An area of locally heavy rain already affecting much of England and Wales as well as parts of Scotland at the start of Friday lingers across these areas through the early hours of Friday and Friday morning.
“Rain is likely to be both persistent and heavy at times. Also a risk of thunder, most likely over parts of England and Wales. This rain will tend to clear from the west through the day, while generally becoming less heavy, and will probably become confined to eastern UK by the end of Friday.
“The public should be aware of a significant risk of localised disruption due to surface water flooding. Lightning may be an additional hazard.”
The warning is valid until 11.50pm on Friday.