DRUGS worth up to £3million have been seized in raids on cannabis factories at luxury homes across west Scotland.

More than 20 homes were raided by police after it was discovered they had been turned into cannabis-growing centres.

Today police revealed a major operation had led to several thousand cannabis plants being seized from a number of cultivation sites, in areas including Glasgow, Ayrshire and Lanarkshire.

Detectives leading Operation League said between 3000 and 5000 plants had been seized, with a street value of up to £3m.

Around a dozen arrests have been made during the three-month operation, including British, Chinese and Vietnamese nationals.

Luxury villas costing up to £750,000 had been turned into sophisticated factories.

Police said additional raids had been carried out in the past few days and many more could be expected during the operation.

Detective Chief Superintendent Stephen Whitelock, director of intelligence for Strathclyde Police, warned the public to be on their guard as the factories could well be in the heart of their communities.

Mr Whitelock said the factories could pose a fire risk to local communities.

He said intense heat was used to cultivate the plants in seemingly-normal three and four bedroom homes which had been ripped apart.

Earlier this month a house in Airdrie was gutted in a blaze - and firefighters found the home was full of cannabis plants.

In some cases around 120 plants have been discovered in what looked like a family kitchen. In other rooms floorboards had been ripped up and walls torn down.

Mr Whitelock added: "We are asking the public to be vigilant and to look out for any clues which may lead them to think this kind of operation is going on."

Tell-tale signs include windows being covered and strange comings and goings late at night.

In some cases people may not live at the premises but will simply turn up to remove the cannabis in bags.

The plants can take just three months to grow.

In the past 10 years, the volume of cannabis produced in the UK has soared from 10% to 60%.

In one raid alone, 800 plants with a street value of £365,000 were seized.