Flood warnings were issued for parts of London and Essex as parts of the capital were expected to see a month's rainfall in a matter of hours on the same day of the historic referendum on whether the country wants to stay or exit from the European Union (EU), the Guardian reported.
London Fire Brigade (LFB) said it received a day's worth of calls in just an hour and a half on weather-related incidents including lightning striking property, flooded homes and businesses and rising waters trapping vehicles.
"Crews are being mobilised to incidents as quickly as possible but the brigade is appealing to people to only call 999 in an emergency - where there is a risk to life or property," an LFB official said.
There were reports of flooded streets as storms swept through, threatening disruption as voters headed to polling stations.
The storm caused major disruption to the capital's travel network, causing problems for thousands of commuters during the morning rush hour.
The Environment Agency has issued four flood warnings covering rivers in Bromley, Sidcup and Basildon and 22 flood alerts across of the country's southeast.
The Met Office issued warning of rain for parts of Kent, Sussex and Surrey.
Conditions are expected to improve for most on Friday although showers will develop across western parts later on.