A blown fuse alerted police to a cannabis factory in Osterley, where they found about 200 plants the size of small Christmas trees yesterday (Wednesday, July 9).
An electrician was replacing a fuse which had blown in flats at Osterley Court, in Great West Road, and became suspicious after it blew again.
He told police he could hear the sound of machinery and water moving in the flat, and could smell cannabis there.
They found two bedrooms and a living room full of cannabis plants, with an estimated street value of £200,000.
No one was at the property when it was raided by police and there have been no arrests in connection with the discovery.
The equipment used to grow cannabis consumes huge amounts of electricity and police are often alerted to cannabis factories by electricity providers.
The heat produced by the plants and equipment also means they can be spotted from the air using thermal imaging cameras.
getwestlondon reported last month how police had arrested three men after discovering a cannabis factory in Isleworth where up to 300 plants, with an estimated street value of £300,000, were being grown.