Charles Clarke is expected today to rule out toughening the law on cannabis despite issuing a fresh warning over the health risk to heavy users.
The Home Secretary will announce a nationwide campaign highlighting the danger of smoking the drug and promise a renewed police crackdown on the cannabis farms that meet the demand for it.
The Government announced a review last year of the decision by David Blunkett, the former home secretary, to downgrade cannabis from a class B to class C substance.
Mr Clarke and Tony Blair were sympathetic to calls to reverse the move, admitting that the change had confused the public about the legal position on drug possession. But they said they would take a decision on the basis of scientific evidence and the Advisory Council on the Misuse of Drugs (ACMD), which carried out the review, did not recommend reclassification.
It concluded that there was a risk of developing schizophrenia through use, but said it said it was "substantially less harmful" than other drugs in the class B category.
Mr Clarke has been warned by some council members that they could resign in protest if he reverses the reclassification, which took place in January 2004.
The Home Secretary will tell MPs this afternoon that he is concerned over evidence of the damage to health from long-term cannabis use. He will promise a fresh publicity campaign highlighting the risks it carries, with particular efforts to get the message into schools. The campaign will also remind the public that reclassification has not made cannabis legal and that possession in large quantities still attracts a two-year prison sentence.
Mr Clarke will also announce a new effort by police to track down and prosecute the country's main suppliers of the drug, who cultivate it in large cannabis farms. They could be imprisoned for up to five years.
Two weeks ago the Home Secretary said he was worried by evidence that the drug could damage mental health and was prepared "in principle" to reverse his predecessor's decision.
He has privately remarked that it is one of the most difficult decisions he has had to take in the job. The political pressure on him over the issue, however, has been eased by the decision of the Tory leader, David Cameron, not to support reclassification.Mr Cameron previously sat on the Commons Home Affairs Select Committee, which supported designating cannabis as class C. The Liberal Democrats support leaving cannabis as a class-C drug and have protested that cannabis users are still being jailed.
The change from class B to class C two years ago was designed to enable police to channel their efforts into tackling use of class-A drugs such as heroin and cocaine.
The switch meant that although possession of cannabis remained illegal, police were advised not to make arrests. They were told to confiscate the drug and give a warning.
Medical experts and drug charities appear divided over the merits of reclassification of cannabis. Martin Barnes, the chief executive of Drugscope, has said. "Our view is that if the Government chooses not to follow the advisory council's recommendation they've got to really have pretty compelling reasons not to."
Lord Adebowale, the director of the drug treatment charity Turning Point and a member of the ACMD, said: "I am increasingly concerned about the politicisation of this - the playing to the gallery."
But the Royal College of Psychiatrists has pointed out that countries with traditionally liberal attitudes to cannabis, such as the Netherlands, are reviewing their laws. It has called on governments to take a "strong stance towards cannabis abuse".
Marjorie Wallace, the chief executive of the mental health charity Sane, said there was mounting evidence cannabis, especially in its more toxic form of skunk, could cause long-term mental damage.
She said: "We do not wish to see more people in prison for possession. But we must balance their interests against those of vulnerable young people, for whom cannabis can mean a life-long sentence to illnesses such as schizophrenia and depression. While we welcome the Home Secretary's renewed pledge to a public education campaign, it will be even harder now to convince young people that by taking cannabis they are playing Russian roulette with their minds."
When Mr Clarke asked the ACMD to investigate the decision to reclassify cannabis he highlighted worries of the link between its use and psychosis. Mr Blair told the Commons: "If it advises us to change that decision, we will do so. If it does not, we will obviously have to consider that."
Ministers pointed out that there had been no increase in cannabis use since it was downgraded. Sir Ian Blair, the Metropolitan Police Commissioner, has said he does not want cannabis laws reversed as dealing with small amounts of the drug wastes police time.Reuse content