A record 4.821 million passengers travelled on the Tube in a single day.
It happened last Friday as Christmas shoppers, theatre and partygoers joined commuters and day-trippers to the capital.
London Underground (LU) announced it was also the busiest week on the system with 28.76 million journeys made.
LU predicted records will keep on tumbling as more and more people pack onto the already overcrowded network.
The previous daily record was set just a week earlier on 27 November with 4.795 people travelling and before that on 9 Ocober with 4.735 passengers recorded.
London is growing faster than any other European capital. Its population of 8.6 million today will become nine million by 2018 and 10 million by 2030.
Nick Brown, LU managing director, said: “The Tube continues to break records for the number of customers we’re carrying as London’s economy and population keeps on growing.”
This year 18 of the top 20 busiest days ever in the network’s 152-year history were recorded.
The figures sparked increasing concern about overcrowding and passenger security.
Manuel Cortes, leader of the TSSA white collar transport union, used the statistics to call for a London security “summit.”
He said: “In the light of these passenger numbers I call on Mayor Boris Johnson, Scotland Yard chief Sir Bernard Hogan and British Transport Police Chief Constable Paul Crowther to meet with heads of the rail unions for a summit on passenger security on the Tube as a matter of urgency.”
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