Britain’s largest ever cannabis-smuggling ring, which operated out of homes and garages in Kingston, Surbiton, Worcester Park, Epsom and Ashtead has been smashed by police after a 14-month undercover surveillance operation.

The network was importing as much as 250 kg of extra-strong skunk cannabis a week from Holland hidden inside flower boxes - worth nearly £1m a week.

Bosses of the “Tesco-sized” network made “grotesque” amounts of money from the lucrative trade - estimated at £70m - but prosecutors admitted the figure may be just the tip of the iceberg.

VIDEO: Dozens of boxes of skunk cannabis smuggled into Surbiton lock-up

Cannabis smuggling gang left £60,000 to rot in a Kingston lock-up

Police discover £196k of drugs money hidden in an attic in Sutton

Bosses of Britain's largest ever cannabis-smuggling ring lived in Kingston and Surbiton

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Some of the bosses had created off-shore bank accounts as far back as 2002 although police believe they started operating in 2006.

Millions of pounds was laundered out of the country through a currency exchange to Dubai and Pakistan where it has since disappeared.

The "board of directors of the network" were making so much money, when police finally swooped they discovered £60,000 in cash rotting away in a damp safe hidden in the floor of a Kingston garage.

But undercover officers cracked the network after a painstaking operation, which followed the bosses into bookies, cafes, and shopping centres, as they dealt with the clandestine business of shifting the cannabis from garages to the major drug dealers who sold it on their behalf.

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Another person was found guilty by a jury at Southwark Crown Court today, minor drug-dealer James Hay from Ashtead, taking the total number of people facing time behind bars to 12.

The three directors of the network pleaded guilty before their trial in November along with several of their underlings.

Police say the men were never forced to resort to violence to protect their trade as they had effectively cornered the market in south-west London and north Surrey.

Officers seized 900kg of the drug - enough to make 225,000 street deals.

DCI Steve Wallace said: "They were making grotesque profits of the back of the addiction this drug reaps.

"They were going on shopping trips to Geneva and Switzerland where they were visiting jewellers and buying expensive watches.

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"When we did the searches we actually found cash rotting away in one of these lock-ups.

"There was so much cash flying around this organisation they just didn’t know what to do with it."

All 12 have been listed for a sentencing hearing on Monday with each of them likely to spend years behind bars as well as facing the prospect of losing their home, cars and bank accounts both in the UK and abroad as police use new laws to confiscate the proceeds of crimes.

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For more see www.surreycomet.co.uk/operationkarnak