Ordering a review into the classification of cannabis was one of Gordon Brown's early acts as Prime Minister, along with reconsidering the decision to allow a supercasino in London, which signalled that his regime would take a much tougher line on social ills. His concern on cannabis was that downgrading it from Class B to Class C sent the wrong message to young people and confused their understanding of drug laws. Now that the Advisory Council on the Misuse of Drugs (ACMD) has recommended that cannabis should remain in Class C, the government's decision to return to Class B is open to the charge of prejudging the issue and following the dictates of populism.

Four-fifths of cannabis seized on the streets is now "skunk", the umbrella term given to several varieties of the plant deliberately bred to produce higher levels of THC, the psychoactive ingredient. There is considerable concern that stronger forms of cannabis make it more likely that users will develop psychotic illnesses including schizophrenia. The advisory council returned a verdict of not proven on this, finding a "probable, but weak, causal link", but it remains a medical controversy, with particular concern about people who start using cannabis at an early age. That gives some justification for the Home Secretary's decision to "err on the side of caution".

The level of classification is designed to reflect harm (and the ACMD argues that cannabis is not as harmful as amphetamines and barbiturates) but the major effect of reclassification is to increase the maximum penalty for possession from two to five years in jail. While that will underline the government's message that cannabis is illegal and harmful, it will cause particular problems for people with chronic illnesses who find it the most effective pain relief. The reclassification will set back their campaign for legalisation and should perhaps open a new consideration of whether cannabis for medical purposes could become available on prescription.

The main argument for downgrading cannabis in 2004 was that it would allow the police to concentrate resources on more serious offences than possession. Since then there has been an increase in cannabis farms, which often use illegal immigrants to tend the plants. That supply chain, involving organised crime, should be the policing priority. One of the best-targeted signals from Ms Smith was that energy companies will be asked to provide information on a consumption pattern that indicates such a factory is in operation.

There is a danger that the dispute over classification deflects attention from other issues. The chairman of the advisory council, Sir Michael Rawlins, a former professor and consultant in clinical pharmacology, has said that the recommendation for a concerted public health programme is more important than the one on classification. He is right. A well-informed programme of education for all young people about the dangers of cannabis use should be the first priority.