Previously the Met Office was only forecasting heavy thunderstorms for parts of Scotland and northern England.
However forecasters are now predicting isolated heavy thunderstorms across parts of England, including some central, eastern and southeastern areas, this afternoon and this evening (Wednesday).
A Met Office spokesman 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.
“This update excludes areas further west where the thunderstorm risk has now diminished, but increases the extent of the warning area across eastern and southeastern England.”
The official weather warning is in place until 9pm this evening.