An editorial in the British Medical Journal suggested that the sale of cannabis should be licensed like alcohol because banning it had not worked.

In fact cannabis related drugs arrests in the US increased from 350,000 in 1990 to more than 800,000 a year by 2006, with seizures quintupling to 1.1million kilogrammes.

The editorial, written by Professor Robin Room of Melbourne University, said: “In some places, state controlled instruments – such as licensing regimes, inspectors, and sales outlets run by the Government – are still in place for alcohol and these could be extended to cover cannabis.”

Prof Room suggested that state-run off licences from Canada and some Nordic countries could provide “workable and well controlled retail outlets for cannabis”.