Milo the sniffer dog helped uncover nearly 3,000 potentially dangerous fake cigarettes in Hounslow.
The spaniel and his companion Indi, a black Labrador, sniffed out 2,700 counterfeit cigarettes, and 22 50g packs of roll-up tobacco at shops in central Hounslow.
Councillor Richard Foote, Hounslow's cabinet member for community safety, said: "Fake cigarettes can be highly dangerous, even more than branded ones, as the smoker doesn't know what's in them.
"Some of the fake cigarettes picked up by trading standards teams across the country have contained asbestos, mould, dust, dead flies, rat droppings and human excrement.
"Many also contain much higher levels of toxic ingredients such as tar, nicotine, carbon monoxide, lead, cadmium and arsenic than genuine brand-name cigarettes."
The operation was carried out last week by two officers from the council's trading standards team, working with the dogs. No arrests have been made but investigations are ongoing.
* For support and advice on quitting smoking, call Hounslow's Stop Smoking Service on 020 8630 3255.
