The warning is a ‘yellow’ level alert with a recommendation to ‘be aware’.
A statement on the Met Office website said: “There is the potential for periods of heavy rain across much of the southern half of the UK from the beginning of Friday until Saturday morning.
“However there remains considerable uncertainty in the northward extent of this heavy rain and the area covered by the Alert is likely to be adjusted further as the event approaches.
“The public should be aware of the possibility of disruption to travel due to localised flooding.”
The warning is in place for the London and South East area from midnight until 6am on Saturday morning.
More information and advice is available online at www.metoffice.gov.uk.