An ex-minister who had responsibility for drugs policy has called for all drugs to be legally available.
Bob Ainsworth, a Home Office minister under Tony Blair, said successive governments' approaches had failed, leaving criminal gangs in control.
The Coventry North East MP wants to see a system of strict legal regulation, with different drugs either prescribed by doctors or sold under licence.
Ministers have insisted they remain opposed to legalisation.
Crime Prevention Minister James Brokenshire said it was "not the answer" to drugs which ruin lives.
"Decriminalisation is a simplistic solution that fails to recognise the complexity of the problem and ignores the serious harm drug taking poses to the individual.
"Legalisation fails to address the reasons people misuse drugs in the first place or the misery, cost and lost opportunities that dependence causes individuals, their families and the wider community."
Poor 'hardest hit'
Mr Ainsworth is the most senior politician so far to publicly call for all drugs, including heroin and cocaine, to be in any way legalised.
He said he realised when Home Office minister in charge of drugs policy that the so-called war on drugs could not be won.
The Labour backbencher said: "Leaving the drugs market in the hands of criminals causes huge and unnecessary harms to individuals, communities and entire countries, with the poor the hardest hit."
Mr Ainsworth said billions of pounds was being spent "without preventing the wide availability of drugs".
"It is time to replace our failed war on drugs with a strict system of legal regulation, to make the world a safer, healthier place, especially for our children," he said.
Mr Ainsworth insisted he was "not a libertarian" and that people should not be encouraged to use substances.
But he said: "We must take the trade away from organised criminals and hand it to the control of doctors and pharmacists."
However, when pressed, he was uncertain as to how any policy might work.
Asked where people might buy cocaine on a Saturday night, he replied: "Maybe at a chemist".
BBC Home Editor Mark Easton said under such a system heroin and cocaine might only be available on prescription from registered doctors, while cannabis might be sold in a similar way to tobacco.
"Those who supplied or sold drugs without the requisite licence would still be operating illegally, in the same way as those who sell tobacco, alcohol or prescription drugs without a licence or proper authority would be currently," he said.
However, none of the three main parties at Westminster supports the widespread legalisation of drugs, although the Lib Dems have said they would eventually like to see cannabis legally available.
A Labour spokesman said Mr Ainsworth's were "not the views of Ed Miliband, the Labour Party or the public". One party source described Mr Ainsworth's comments as "irresponsible".
When asked why he did not make the call while in government, Mr Ainsworth said: "I did what I could within the confines of collective responsibility."
He said David Cameron had called for examination of alternatives to prohibition when a member of the Home Affairs Select Committee but dropped the suggestion on becoming Conservative leader.
Fear of a media backlash prevented politicians from arguing for a change in policy and a "grown-up debate" was needed, said Mr Ainsworth.
"As you can see from the reaction this morning, if I was now a shadow minister, Ed Miliband would be asking me to resign. If one of David Cameron's ministers - despite the fact [the prime minister] probably agrees with me - agreed publicly with me, he would have to resign."
Last week, Home Secretary Theresa May said the government's drugs strategy would remain focused on rehabilitation and reducing supply.
However, former chief constable of Cambridgeshire Police, Tom Lloyd, said something had to change.
"We've got so used to 40 years of prohibition which, in my experience of over 30 years of policing, has led to massive cost, a failure to achieve the primary aims, which is the reduction of drug use, and a range of unintended harmful consequences," he said.
The former chief adviser to the government on drugs, Prof David Nutt, told the BBC that most MPs actually agree with Mr Ainsworth, but feel they cannot say so publicly because of "the pressure of politics".
Prof Nutt said that in other countries such as Holland, where cannabis is legal, there have been several benefits.
"It's reduced cannabis use and the harms of cannabis, and it has separated the heroin market from the cannabis market.
"In this country if you want to use cannabis you will inevitably get in contact with a dealer who will always be trying to push on you the harder drug."
However, anti-drugs campaigner Debra Bell, whose eldest son William began smoking cannabis at 14, believes that he would have progressed to taking class A substances had they been legally available.
"Just the fact that Bob Ainsworth is talking in this way will send strong signals to some children - a green light - to start experimenting and I really don't think that's the way forward in a civilised society," she argued.