Police figures reveal that the number of marijuana plants and amount of resin seized have increased dramatically across the country, even though cannabis was reclassified to allow forces to concentrate on hard drugs such as heroin and cocaine.

In Strathclyde, seizures of home-grown plants have more than doubled in the last year and in Tayside there has been a sixfold increase. Police warned that the cultivation of the drug had increased because of a misconception among members of the public that they would not be prosecuted.

On January 29, 2004, David Blunkett, the former home secretary, reclassified cannabis from a class B to a class C drug.

Academics, including Professor Neil McKeganey, of the Centre of Drug Misuse at Glasgow University, warned against the move because they believed it would lead to an increase in use.

Yesterday, officers said those fears had been realised with an increase in the cultivation and smoking of a drug which has been shown to trigger mental health problems. The price of cannabis resin has also fallen, another indication of its growing availability.

New figures obtained by The Herald show that between April 2003 to 2004 there were 742 plants seized in Strathclyde, compared with 1715 between April 2004 and December 2004. There was also a 14% increase in the amount of cannabis resin and material seized by the force, despite the fact there are still three months left in the statistical year.

In Fife, the amount of cannabis resin seized rose in that period from 36kg to 329kg last year, while plant seizures rose from 280 to 362.

There was also a significant increase in plant seizures in Lothian and Borders.

A report commissioned by the Metropolitan Police Authority last year found that many people wrongly believed the drug had been legalised following its reclassification.

Detective Sergeant Kenny Simpson, the Strathclyde Police drugs co-ordinator, said: “The figures are significantly up and the issue seems to be that a lot more people are growing their own because of their perception that police activity has been relaxed. There is also concern that home-grown cannabis, or skunk, can be three times as strong as resin. There are substantial health risks associated with this.

“Our message is that we will not ignore this. We will take action and will prosecute these people.”

Detective Superintendent Jill Wood, national drugs co-ordinator for the Scottish Drugs Enforcement Agency, said the national figures indicated that cannabis cultivation had increased. “The trends show that all the forces are seeing an increase in the number of cannabis plants being recovered.”This would indicate that this is more than just an increase in police activity. For most forces cannabis would not form part of their main targets. However, we will continue to take action and devote resources to this. The reclassification has not changed our practice.”

Alistair Ramsay, of Scotland Against Drugs, said the growing misconceptions about cannabis had to be corrected. “This is a very worrying development which will mean more cannabis is available in communities around the country.

There is clearly a misunderstanding about its illegality.” The Scottish Executive said: “There is a perception that cannabis is safe and has been decriminalised for personal use. That perception is a myth.

Cannabis is not safe, it brings risks to both physical and mental health.

“Recently there has been new research published which appears to reinforce the risks to mental health. Sustained use of cannabis can create dependence.

“Around 10% of people reporting to drug services say cannabis is their main problem drug. That is why it is important to reinforce the message that reclassification is not the same as decriminalisation or legalisation.

“Possession and supply of cannabis are criminal offences. They remain criminal offences. The maximum penalty for supplying has been increased to 14 years’ imprisonment.”