The Food Standards Agency was alerted by a member of the public who complained to Diageo - the distributor of Johnnie Walker Black Label - which confirmed that the product was not genuine as both the packaging and liquid are counterfeit.
The Agency has no information on the source or origin of the product or possible distribution.
So far, 50 counterfeit bottles have been found on sale all in the Hackney area of London. But it is possible that the whisky is on sale elsewhere in the country, the FSA said.
Tests showed that the whisky had been contaminated with unacceptable levels of methanol.
Head of chemical safety and toxicology at the FSA, Andrew Wadge, said: “At these levels detected, consumers would be at risk of harmful effects including severe stomach pain, vomiting and blindness.”
A Food Hazard Warning has been issued to all local authorities across the UK asking them to ensure the product is not on sale in their area.