Trading standards officers confiscated 75 packets of condoms from three shops.
The Medical & Healthcare Products Regulatory Agency (MHRA) has been brought in to help discover where the fakes came from. Seven brands of fake three-packs are believed to be in circulation in London.
Counterfeit condoms can be identified by looking at the packet's batch number. Durex, which allocates a batch number to each packet, confirmed the numbers were false and had not been issued by the company.
Camden's executive member of environment Mike Greene (Con) said: "We would urge residents to buy condoms from a reputable chemist. We would also encourage shopkeepers to buy condoms from legitimate sources or face a hefty fine."