Police have prevented drugs worth between £600,000 and £1.2 million getting onto the streets of Hounslow after raiding a third cannabis factory in just over a month.
PC Tom Blair, of Hounslow Neighbourhood Policing Team, who was involved in all three raids, said the estimated street value of a single cannabis plant ranged from £1,000-2,000, depending on its type and size.
"There have been a significant number of plants at all these factories, which adds up to a hell of a lot of drugs which have been kept off the streets," he added.
"Closing these factories disrupts organised crime networks and helps prevent other crime and antisocial behaviour associated with cannabis. That is why we need you to get in touch if you suspect cannabis is being grown near you."
Although all three farms were found in or around Isleworth, Mr Blair said it was too early to say whether the area had a particular problem with cultivation of the class C drug.
The plants discovered yesterday, just off Great West Road, near Syon Lane station, may have been little more than seedlings, but Mr Blair described those unearthed on Wednesday as the biggest he had ever seen.
A police spokesman said the cultivation of plants at the latest property to be raided had caused a substantial amount of damage, possibly due to the way the equipment was wired up.
Nobody has been arrested in connection with the two factories raided this week, though police said enquiries were ongoing. No further action was taken against the three men arrested in June, following an investigation.
* If you suspect cannabis is being grown near you, call police on the non-emergency number 101 or call Crimestoppers, free and anonymously, on 0800 555 111.
Six tell-tale signs of a cannabis farm
* a strong, sickly sweet smell
* constantly covered windows, especially those with foil coverings
* strong and constant lighting, day and night
* high levels of heat and condensation misting up windows
* lots of power cables or lighting and ventilation equipment
* constant buzz of the ventilation system