Police were finding one large factory a month in the borough until September 2009, when the rate almost trebled and another 10 were discovered in the final months.

In total, Sutton police discovered thousands of plants in 2009 with a street value of millions of pounds.

One of the largest crops found was in a semi-detached house in Onslow Gardens in September.

Police were tipped off by suspicious neighbours who had been alerted by boarded up windows and strange smells coming from the house.

The house was raided and the occupants, Pham Van Hoy and a 16-year-old Vietnamese national, who cannot be named for legal reasons, tried to escape from a side window where he ran into a waiting dog unit.

Officers found about 600 plants in the house with a street value of £300,000.

Hoy, 26, was tried at Croydon Crown Court last week and was also found guilty of stealing £13,000 of electricity from a unsuspecting neighbour.

On February 1, he was sentenced to two years behind bars.

His accomplice is still awaiting trial at Croydon Youth Court.

Hoy, a former Vietnamese fisherman, had a history of immigration-related problems and initially denied the charges but later pleaded guilty.

Inspector Chris Riggs, of Sutton Police station, said: “Drug-related crime will not be tolerated in our communities and we urge the public to remain vigilant and to report suspicious activities to us.”

Police are asking residents to report comings and goings of occupiers at odd times of the day and night, permanently closed curtains – which hide the blazing lights required to grow the plants – or sweet smells emanating from the property.

If you suspect that a property could be a cannabis factory call Sutton police on 0300 123 1212 or Crimestoppers, anonymously, on 0800 555 111. SOME FACTORIES DISCOVERED IN 2009. q February: Police found a factory in a £750,000 home in Champneys Close, concealing six rooms full of large plants. The electricity supply had been rewired to bypass the meter, work that had involved digging up the road. q March: Gardening magazines found in a privately-owned house in Mulgrave Road, Sutton, which also contained more than 200 plants with an estimated value of £15,000. q June: Sutton police community support officers (PCSO) stumbled across another factory in Hazelmere Gardens in Worcester Park. They found 140 cannabis plants in the garden worth more than £70,000. q August: Two landlords returned to their exclusive four-bedroom property in Lenham Road after it went up in smoke, to find it had been turned into a cannabis farm, which had 500 plants worth in excess of £250,000. q September: A crop of cannabis with a street value of £50,000 was seized in a police raid in Poulton Avenue, where a total of 221 plants, and equipment used in their cultivation, were seized by officers.