Legalising the sale of cannabis could raise £1 billion a year in tax and help minimise health risks, according to a report.
The study, commissioned by the Liberal Democrats and conducted by a panel of scientists, academics and police chiefs, suggests that the drug should be available in specialist shops to over-18s. The party is expected to debate the issue at its spring conference later this week.
Lib Dem health spokesman Norman Lamb said: "Every year billions of pounds are put into the pockets of organised criminals selling cannabis and vast amounts of police time and resources are wasted going after those using the drug."
Party leader Tim Farron said: "Prohibition of cannabis has failed. We need a new, smarter approach and I welcome this report ahead of the Liberal Democrats' debate at spring conference.
"It is a waste of police time to go after young people using cannabis and ludicrous to saddle them with criminal convictions that can damage their future careers. A legal market would allow us to have more control over what is sold, and raise a considerable amount in taxation."
Panel chairman Steve Rolles said: "The reality is that millions of people use cannabis in the UK and there is a pressing need for government to take control of the trade from gangsters and unregulated dealers.
"Legal regulation is now working well, despite the fear-mongering, in Colorado and Washington and will roll out across the US over the coming years. This is no longer a theoretical debate - and the emerging evidence is only pointing in one direction."