Professor David Nutt endured a bruising encounter with MPs on the home affairs committee today, as he made the case for the decriminalisation of drug use.
The expert, who was removed from the advisory committee on drugs by then-home secretary Alan Johnson, spoke to the committee ten years after it published a report saying enforcement policies were "destined to fail".
Professor Nutt told MPs: "We've had 100,000 Mexicans dead in the last ten years but no change.
"What I am interested in is the net benefit to society of having rational drugs laws.
"Most South American governments agree with us - the criminalisation approach isn't solving the problem.
"We'll never win the war on drugs."
MPs from all parties attacked the drugs experts. Some said they were offended by his attempt to compare the harm of cannabis and alcohol, but he won a sympathetic hearing from Liberal Democrat MP Julian Huppert and some others.
Professor Nutt also argued that the prohibition of recreational drugs was discouraging research onto their potential medical uses, particularly in mental health.
"What we have discovered is that when drugs become illegal people stop researching them,"he said.
"We've just done the first study of Psilocybin [the psychoactive compound found in magic mushrooms] and we discovered it might be useful for depression.
"We haven't discussed these drugs which have profound brain effect, because the regulations make it impossible."
An experiment into the use of MDMA, the active ingredient in ecstasy, for post-traumatic stress disorder among British troops is currently being undertaken. But even if its results are positive doctors will not be allowed to prescribe the drug.