Deputy Prime Minister Nick Clegg claims Britain is losing the war against drugs on an industrial scale and insists laws need to be reformed - a position at odds with the prime minister.
The leader of the Liberal Democrats said the prime minister needs to show courage over the debate on drugs, after David Cameron ruled out a review into the government's approach earlier this week.
In an interview with the Sun, Mr Clegg said: "If you were waging any other war where you have 2,000 fatalities a year, your enemies are making billions in profit, constantly throwing new weapons at you and targeting more young people, you'd have to say you are losing and it's time to do something different.
"I'm anti-drugs - it's for that reason I'm pro-reform."
He insisted he is not in favour of full legalisation of drugs but thinks targeting dealers and traffickers, while decriminalising possession, might be a solution.
A missed opportunity?
The Commons Home Affairs Committee found the government's drugs policies to be failing in a report published on Monday, and recommended a royal commission to look at alternatives.
Mr Clegg told the Sun he will include a "clear commitment" to a royal commission on drugs in his party's 2015 manifesto.
He added: "I told the prime minister that this was a missed opportunity. He knows my views on this. He and I don't agree on this."
The Lib Dem leader said he has ordered Home Office minister Jeremy Browne to compile a report on liberal approaches to drugs across the world which have worked, including in Portugal, Amsterdam, Latin America and several US states.