Cannabis should be legalised to bring the UK up to speed with a growing number of Western countries and end the "embarrassment" of domestic drugs policy, MPs have said.
Lib Dem former deputy prime minister Nick Clegg and former health minister Norman Lamb have joined Labour and Tory figures to back a new report which claims legalisation of the class B drug could net the Treasury more than £1 billion a year in tax revenue.
The Adam Smith Institute and Volteface study argued that the UK should follow the lead of the United States, where four further states legalised marijuana in this month's elections.
The report argues that Britain's "dark ages" drugs policy has failed to stop drugs being manufactured and used, and also failed to stop the associated crime, corruption, and killing.
It comes as Germany gets ready to legalise cannabis for medical purposes and Canada prepares for all-out decriminalisation.
The Netherlands effectively decriminalised cannabis decades ago while Portugal legalised it in 2001.
It is thought a legal cannabis market could be worth £6.8 billion to the economy annually, potentially netting between £750 million and £1.05 billion in tax revenues and reduced criminal justice costs.
The number of offenders in prison for cannabis-related offences in England and Wales would also likely drop from the current 1,363, who cost taxpayers £50 million a year, the report said.
Mr Clegg said: "Cannabis prohibition is being swept away on a tide of popular opinion and replaced with responsible legal regulation.
"Now is the time for ministers to start writing the rules for this legal market, including age limits and health warnings, so that we can finally take back control from the criminal gangs."
His Liberal Democrat colleague Mr Lamb added: "Prohibition is harmful and counter-productive, helping neither to reduce drug use nor the risks to public health.
"While other countries and US states are increasingly coming to adopt a more enlightened approach to drug policy, we are stuck in the dark ages, filling the pockets of criminals and perpetuating the stigma which prevents so many drug users from seeking help."
Conservative former cabinet minister Peter Lilley said: "It is time we legalised cannabis. Currently cannabis can only be obtained from illegal gangs who also push hard drugs. So we are driving soft drugs users into the arms of hard drugs pushers."