The Government's chief drug adviser sparked controversy yesterday by claiming ecstasy, LSD and cannabis are less dangerous than both alcohol and cigarettes.

Professor David Nutt, chairman of the Advisory Council on the Misuse of Drugs, attacked the decision to make cannabis a class B drug.

He accused former Home Secretary Jacqui Smith, who reclassified the drug, of "distorting and devaluing" scientific research.

Prof Nutt said smoking cannabis created only a "relatively small risk" of psychotic illness.

And he claimed advocates of moving ecstasy into class B from class A had "won the intellectual argument".

All drugs, including alcohol and tobacco, should be ranked by a "harm" index, he said, with alcohol coming fifth behind cocaine, heroin, barbiturates, and methadone.

Tobacco should rank ninth, ahead of cannabis, LSD and ecstasy. Prof Nutt said: "No one is suggesting that drugs are not harmful. The critical question is one of scale and degree."

He repeated his claim that the risks of taking ecstasy are no worse than riding a horse.