The streets of Sussex have been swamped with powerful new strains of cannabis since the drug was downgraded, it has emerged.

There is more than twice as much skunk available following an explosion in production since cannabis was reclassified from a Class B to Class C drug in January 2004 - and scientists claim it has doubled in strength.

Dozens of homes across the county have been turned into "farms" packed with plants since the Government's controversial decision to relax the laws on cannabis.

They are often run by South-East Asian crime syndicates, mostly from Vietnam, with the potential for rich pickings.

A domestic factory can produce £500,000 worth of drugs a year but cost as little as £20,000 to set up.

Detective Sergeant Tony Pike, of Sussex Police's Serious and Organised Crime Unit, told The Argus the number of "hydroponic" factories, where people had blackened the windows in sheds, back rooms and at times entire houses so they could artificially grow a high yield of stronger plants, had soared which in turn led to much more of the drug making its way to the streets.

Criminal gangs are attracted to cannabis production because it is seen as low risk compared with the Class A drug trade. A crop of 200 cannabis plants in a typical domestic factory could produce as much as £30,000 worth of skunk every three months.

In October 2006 370 plants were discovered at an office in Hastings and the July before 114 plants with potential yield of 9.5 kilos were found in the loft of a home in Haywards Heath - which could have been worth up to £100,000 on the street.

Det Sgt Pike said: "Since the re-classification we have seen a noticeable increase in the amount of skunk being grown on a commercial scale for sale and profit.

"Evidence of so-called hydroponics factories are coming in thick and fast now whereas when I joined the drugs squad 11 years ago it was very rare. I would say it happens more than twice as much now.

"I think it is because more dealers and suppliers find there is just as much profit in cannabis as harder drugs like cocaine and heroin but the risk is lower.

"With more experts around the strength and quality of the skunk is also higher. It is well known that skunk cannabis is twice as strong as normal cannabis or resin."

Skunk is up to seven times stronger than normal cannabis and is linked to psychosis, depression and anxiety.

In the mid-Nineties, only around 10 per cent of cannabis in the UK was skunk but in the last decade that figure has risen to around 60 per cent.

Larger factories are capable of producing nearly £500,000 of the drug every year. Bigger farms in industrial or agricultural units can have over 1,000 plants and generate up to £8million a year.

Two scientific studies recently found that there were higher levels of psychoactive agent THC in samples of skunk seized by police in Sussex.

Analysis had shown average content of the active ingredient had risen from seven per cent in 1995 to 14 per cent in the most recent tests which means smoking it is more damaging to the health than in the past.

Det Sgt Pike said: "The dangers of cannabis have increased according to a lot of scientific reports which link it to mental illness and things like that.

"It is also a big concern because cannabis is a gateway drug to things like cocaine and heroin and so the more cannabis there is on the streets the more people will be making that step."

The Argus spoke to a teenager who attributed his mental breakdown in part to cannabis.

Craig - not his real name - had started smoking pot when he was 11, and by his late teens was smoking heavily from morning until night. At the height of his breakdown he had sought help from his GP, only to be told bluntly: "Just stop smoking it".

But for Craig, giving up wasn't that easy. Eventually, his worried family clubbed together to pay the £16,000 fees for a place at the Priory Clinic in Hove.

Craig is now doing well, but not everyone can afford to pay for a private rehabilitation programme.

Martin Barnes from drug information charity Drugscope said there was no doubt that skunk had become more potent in recent years but he did not think it was down to the reclassification.

He said 60 per cent of skunk on the streets was now grown in the UK while the figure had been 10 per cent ten years ago. He said the home-grown versions of the drug was grown in a different way which seemed to make it stronger and had replaced resin and other forms of grass imported from other countries after more restrictions were introduced abroad.

Mr Barnes said: "Levels of potency have increased but I do not think there is less risk for dealers. I have not come across any evidence of a lighter touch in charging dealers - the law is just softer in terms of possession."

David Lepper, MP for Brighton Pavilion, said he was very impressed with the work Sussex Police were doing to uncover so many of the drugs factories in raids and believed the reclassification of cannabis three years ago may have been a mistake.

He said: "Gordon Brown has already signalled a rethink on that classification and I think there is a good case for re-classifying cannabis as a Class B drug once again.

"It is interesting that the Independent newspaper led a campaign for legalising the drug and are now saying they got it wrong. I think a lot of people are looking at the evidence and re-thinking the matter."

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