Nick Clegg has said drug users should not be criminalised, but critics say he is out of touch with the damage drugs do.
In a joint article with businessman Richard Branson in The Guardian, Clegg says all politicians should “embrace the call for reform”.
However, the idea was described as “deeply irresponsible” by an anti-drugs group which pointed out that decriminalisation would make children think drugs are safe.
Mary Brett, from Cannabis Skunk Sense, said: “Nick Clegg demonstrates complete ignorance of the facts on drugs like cannabis and skunk.
“There is overwhelming evidence of a link between skunk and mental health problems like psychosis and schizophrenia.”
The Centre for Social Justice think-tank said that many charities that work with the fallout of drug addiction are against weakening drugs laws.
“Many are right to be worried that liberalising cannabis laws will lead to more people taking drugs and developing harder use.
“Politicians need to listen to these experts. They are the people who witness the devastating impact of drugs in our poorest neighbourhoods day in, day out”.
In their article, Clegg and Branson attack the current British model, saying “prison cells are still used for people whose only crime is the possession of a substance to which they are addicted”.
They call for a Portugal-style system where: “Drugs remain illegal and socially unacceptable, as they should be, but drug users are dealt with through the civil rather than the criminal law.
“Anyone who is arrested for drug possession is immediately assessed and sent for treatment or education. If they fail to engage, they have to pay a fine.”
In Portugal, the number of children who used drugs in the decade after the law was liberalised doubled, according to 2011 figures from the European School Survey Project on Alcohol and Other Drugs.