The Met Office has extended the yellow warning for heavy rain and thunderstorms across the whole of East Anglia.
Its warning of the risk of localised flash flooding and hail along with potential for disruption to travel and power supplies.
The weather warning is valid until 9pm on Wednesday 20 July 2016
The Met Office says areas of heavy thunderstorms will continue to affect parts of Scotland and northern England into this afternoon before slowly clearing away northeast.
However isolated heavy thunderstorms may still develop across Scotland and parts of England, including some central, eastern and southeastern areas, this afternoon and this evening.
The Met Office said: "Whilst most places will miss the worst, please be aware of the risk of localised flash flooding. Frequent lightning, large hail and strong winds could be additional hazards. All of this could lead to some flooding of homes, businesses and transport networks. Disruption to power is also possible."
"Hot, moist air spreading north and northeast across the UK today will produce thunderstorms, initially organised within large areas of rain before becoming more isolated this afternoon.
"Rainfall will be very variable, but some places could see around 30 mm in an hour and more than 50 mm in a few hours.
"The thunderstorms later this afternoon are likely to be most widespread across northern England and Scotland, and it is here that there is the greatest risk of disruption.
"Further south, they will be much more isolated, with disruption less likely, across the rest of England."
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