Cannabis is to be reclassified as a Class B drug after an official review this spring, The Times has learnt.

Gordon Brown and Jacqui Smith are determined to reverse the decision to downgrade the drug when the Advisory Council on the Misuse of Drugs completes its report in the next few months.

While its recommendations are not yet known, ministers are already making plain that the Home Secretary is prepared to overrule the expert body if necessary.

Reclassifying cannabis as a Class B drug will mean that anyone found in possession of the substance could face a five-year jail term and an unlimited fine rather than a police warning and confiscation of the drug. The penalty for supplying would remain the same, at a maximum 14 years in jail and unlimited fines.

The advisory council, which rejected a previous attempt to reclassify cannabis in 2006, has been told to take into account public attitudes to cannabis as well as the medical evidence of its harm in reaching its conclusion.

Ms Smith wants the council to acknowledge the signal that the reclassification of cannabis from Class B to Class C in 2004 sent to the public, including the perception that the drug was harmless and even legal.

“The sentiment from No 10 and the Home Office is very much towards reclassification. It has to be as much about the message that is being sent out as much as anything else,” a senior Whitehall figure has told The Times. The growth of super-strength “skunk”, herbal cannabis that is grown under lights, often by organised criminal gangs, is strengthening ministers’ resolve to restore its Class B status.

New evidence on the harm to mental health that smoking stronger forms of cannabis can cause helped to prompt the latest review of the law last autumn.

In her letter to Professor Sir Michael Rawlins, the chairman of the council, requesting a further review of evidence, Ms Smith said: “Though statistics show that cannabis use has fallen significantly, there is really public concern about the potential mental health effects of cannabis use, in particular the use of stronger forms of the drug, commonly known as skunk. This is in addition to the longitudinal studies undertaken in New Zealand and the Netherlands that link cannabis use to mental health problems.”

Suggestions that only the most potent forms of cannabis be reclassified are rejected as impractical. Instead offenders may be allowed to use evidence showing they were caught with milder forms of the drug in mitigation, Home Office insiders contend.

Shortly after becoming Prime Minister Mr Brown signalled his desire to reverse David Blunkett’s 2001 decision to reduce cannabis to a Class C drug that came into effect three years later.

“It is the message you send out. Why I want to upgrade cannabis and make it more a drug that people worry about is that we don’t want to send out a message, just like with alcohol, to teenagers that we accept these things.”

The council makes recommendations to the Government on the control of dangerous or otherwise harmful drugs, including classification and scheduling under the Misuse of Drugs Act 1971. Its last review came down against tightening up the penalties for using cannabis, saying there was too little information about the pattern of use of different strength cannabis products by users to change the law.

The council has recently been highly critical of parts of the Government’s consultation paper on the future of its drug strategy. “It is disappointing that the paper makes no mention of needing to improve the evidence base of drug misuse and treatments nor makes use of international evidence, for informing and guiding policy,” the council said.

The unpublished results of authoritative research into cannabis confirm that the skunk now on sale in England is stronger than it was a decade ago, but demolish claims that a new super-strength skunk, which is 20 times more powerful, is dominating the market.

The two studies due to be published this year, which together analysed nearly 550 samples of skunk seized by the police, both conclude that the average content of the main psychoactive agent in skunk strains of cannabis, THC, has doubled from 7 per cent in 1995 to 14 per cent in 2005.

Another dilemma for the Government in defending a decision to press ahead with reclassification is that the latest figures from the British Crime Survey suggest a long-term fall in cannabis use. Figures from the 2006-07 survey estimate that 20.9 per cent of 16 to 24-year-olds used cannabis in the past year. However, there has been a decrease between 1998 and 2006-07 among 16 to 59-year-olds in the use of cannabis from 10.3 per cent to 8.2 per cent.

Buzzwords: smoker’s choice of the highs and lows

Afghan cannabis
This strain was imported from Afghanistan originally and bred selectively in the Netherlands for indoor cultivation. It has a strong, acrid aroma. The smoke is heavy with a strong, almost numbing buzz

Dutch dragon
The aroma is very citrus and sweet, similar to tangerines, as is the taste. The buzz is a lasting, clear high that allegedly increases an appetite for music and pleasure

Moroccan cannabis
This is generally of poor quality, with cannabis resin from Morocco varying from a 2 per cent purity to about 8 per cent

Herbal cannabis
This is produced by drying the leaves and flowering buds of the cannabis plant. It is smoked, usually with tobacco, in a spliff or joint

Skunk
A very potent variant of herbal cannabis, both in its mind-altering effects and its aroma, it contains more tetrahydrocannabinol, the main psychoactive agent in cannabis

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