Group including former government adviser and ex-chief constable will consider how a legal market for cannabis could work in Britain

The Liberal Democrats are to set up an expert panel to establish how a legal market for cannabis could work in Britain, paving the way for them to become the first major political party in the UK to back its legalisation.

The move is backed the party’s health spokesman, Norman Lamb, and by a former deputy assistant commissioner of the Metropolitan police, Brian Paddick. It is in line with a 2014 party conference resolution which called for a review of the effectiveness of a regulated market in relation to health and reduced criminal activity.

The review panel members will include Prof David Nutt, the founder of DrugScience and a former chairman of the government’s advisory committee on the misuse of drugs, Tom Lloyd a former Cambridgeshire chief constable and chair of the National Cannabis Coalition, and Niamh Eastwood, the executive director of Release, a drugs charity. The panel is to be chaired by Steve Rolles, of the drugs policy campaign group Transform.

Lamb wants the expert panel to look at evidence from Colorado and Washington State, in the US, where cannabis has been legalised since 2012, and from Uruguay, and to make recommendations for the party’s conference next spring. He says a move to a legal cannabis market in Britain must be based on international evidence and include effective regulation to minimise the harm that cannabis can cause to health.

He said: “I share people’s concerns about the health impacts of any drug – legal or illegal. But we can better manage that harm by taking the money that’s currently spent on policing the illegal cannabis market and spending it on public health education and restrictions at the point of sale.

“That’s the approach we have taken with cigarettes and it has led to dramatic reductions in smoking in recent years.”

Lamb said the recent emergence of successful legal cannabis markets in different parts of the world meant the onus was now on the supporters of prohibition to explain why it shouldn’t happen in the UK.

“We must end the hypocrisy of senior politicians admitting to using cannabis in younger years – and describing it as ‘youthful indiscretions’ – whilst condemning tens of thousands of their less fortunate fellow countrymen and women to criminal records for precisely the same thing, blighting their careers.”

Lord Paddick led a pilot scheme in Lambeth 10 years ago which effectively decriminalised cannabis for personal use for a 12-month period. It demonstrated that the police saved resources, enabling them to deal more effectively with serious crime, and crime fell significantly over the period.

On Monday, MPs are set to debate the legalisation of the production, sale and use of cannabis as a result of a petition to parliament which has attracted more than 221,000 signatures.

A briefing for the debate by Transform says four US states – Alaska, Colorado, Oregon and Washington – and the capital, Washington DC, have legalised cannabis for non-medical adult use.

It says legalisation in Colorado, where retail shops opened for the first time last year, has not led to a spike in cannabis use among young people, but has led to a large reduction in the criminal market, with the state now controlling 60% of sales. The predicted tax take for 2015 is $125m (£81m), of which $40m is to be allocated to school building programmes.

The home secretary, Theresa May, has repeatedly ruled out any relaxation of the UK’s cannabis laws. The Home Office maintains that the long-term downward trend in drug misuse is evidence that the official drugs strategy is working.