In the early afternoon the temperature on the roof of the London Weather Centre reached 15.7C - just over 60F. The previous record was 15.2C, set in 1940, while a temperature of 15.6C was recorded at Kensington Palace in 1922. The record goes back to 1841.
Meanwhile, heavy rains caused chaos and flood alerts in parts of the north-west.
Other parts of the south were also very warm, with Gravesend in Kent reporting an afternoon temperature of 15.9C and Bournemouth one of 13.8C.
The mild weather has been caused by warm air from the Azores flooding into Britain behind a cold front which has been stationary over the north of the country for several days.
But last night rain and colder air was coming in from the west.
The record temperatures yesterday could not be attributed to global warming, said a spokesman for the Met Office.