In January 2004 cannabis was downgraded to a class c drug in the UK.
Medical experts at the Advisory Council on the Misuse of Drugs (ACMD) had said the old classification of cannabis alongside substances like amphetamines was "disproportionate" to its harmfulness.
The Tory leader at that time, Iain Duncan Smith said downgrading or decriminalising cannabis would be an ill-thought out solution to a complex problem. During a visit to Langdon College in Salford he said: "Anybody who knows about the difficulties in communities, about young people who are trying drugs and moving on to harder drugs, knows it is far more complex than that."
ACMD chairman Professor Sir Michael Rawlins said his report was not saying cannabis was harmless.
"Cannabis is associated with some risks of health but the council concludes that these are less than the risks posed by other Class B drugs such as amphetamine," he said. The report found the use of cannabis, which has risen sharply over the past 29 years, does not cause any major health problems and rarely causes serious illness in previously healthy people.
The reclassification of cannabis as a Class B drug came into effect in England and Wales in January 2009 amid complaints the new laws were "illogical".
Ministers went against their own advisors to upgrade the drug.