More than 20,000 London restaurants, cafes and food shops failed environmental health inspections in the year to 31 March 2005.
While more serious food hygiene breaches can lead to fines or closure, the Food Standards Agency stressed that the majority cases involved minor offences.
A spokeswoman said that over the same period 96% of enforcement action taken against restaurants nationwide took the form of improvement notices.
It was closely followed by Kensington and Chelsea (with 1,677 enforcement actions), Southwark (1,239), Tower Hamlets (1,151), Hammersmith and Fulham (1,087) and Enfield (1,039).
The lowest level of food safety and hygiene offences was found in Lambeth (with no cases), the City of London (16) and Ealing (49).
By Angela Frewin