The Government’s chief drug adviser has suggested that Ecstasy, LSD and cannabis are less dangerous than both alcohol and cigarettes.

David Nutt, chairman of the Advisory Council on the Misuse of Drugs, attacked the decision to make cannabis a Class B drug. He accused the former Home Secretary Jacqui Smith, who reclassified the drug, of “distorting and devaluing” scientific research.

Professor Nutt said smoking cannabis created only a “relatively small risk” of psychotic illness, adding that all drugs, including alcohol and tobacco, should be ranked by a “harm” index.

He said that alcohol came fifth behind cocaine, heroin, barbiturates and methadone, while tobacco should rank ninth, ahead of cannabis, LSD and Ecstasy. His views are published today as a briefing paper for the Centre for Crime and Justice Studies at King’s College London.

It is not the first time that Professor Nutt has courted controversy. He first recommended the introduction of a drugs’ harm scale in a paper in The Lancet in 2007, when he also suggested that alcohol would rate higher than substances such as LSD. Earlier this year he suggested that the dangers of taking Ecstasy were no greater than those of frequent horse riding, which he repeats in the latest paper.

Professor Nutt attacks the “artificial” separation of alcohol and tobacco from illegal drugs. “No one is suggesting that drugs are not harmful. The critical question is one of scale and degree.

“We need a full and open discussion of the evidence and a mature debate about what the drug laws are for — and whether they are doing their job.”

The paper — Estimating Drug Harms: A Risky Business? — criticises the decision to increase penalties for supplying Class C drugs. The move to double the maximum prison sentence from seven to 14 years was taken as a “tit-for-tat” move when cannabis was downgraded, Professor Nutt said.

In recent years drug classification policy has become “quite complex and highly politicised”, he said. The Advisory Council on the Misuse of Drugs’ (ACMD) review of cannabis classification, ordered in 2007, was the result of a “skunk scare”, he claimed.

Overall, cannabis users faced a “relatively small” risk of getting a psychotic illness compared with the risks of smokers contracting lung cancer. Ms Smith’s decision to reclassify it as a “precautionary step” sent mixed messages and undermined public faith in government science, he said.

He added: “I think we have to accept young people like to experiment — with drugs and other potentially harmful activities — and what we should be doing in all of this is to protect them from harm at this stage of their lives.

We therefore have to provide more accurate and credible information. If you think that scaring kids will stop them using, you are probably wrong.”

James Brokenshire, the Conservative home affairs spokesman, said that Professor Nutt’s comments only added to the confusion over drug classification.

“Giving simple labels of levels of harm risk gives a false impression of the dangers,” he said. “Drugs like GBL [a ‘party’ drug] can be lethal if taken in combination with alcohol.

“Rather than providing clearer evidence on the harms linked to illicit drugs, Professor Nutt is making an overtly political pitch and that isn’t helpful.”

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