By Dominic Casciani
BBC News, Home Affairs
David Nutt: Scientist who clashed with policy
Professor David Nutt has been sacked as the government's top drugs adviser after a rollercoaster of a relationship with two home secretaries over the last 12 months.
It was his job to provide hard scientific facts to the government on the harm of drugs. But he has left the unpaid post under a cloud after ministers concluded the psychiatrist and pharmacologist's analysis went beyond scientific facts and into the realms of attempting to change policy.
Based at Imperial College London, the professor is one of the country's leading experts on the effect of drugs.
He is also deeply involved in community medicine programmes in NHS trusts in south-west England and has long-standing links with Bristol University.
Decade with drugs body
Prof Nutt first became involved in official drugs policy at the Advisory Council on the Misuse of Drugs (ACMD) a decade ago.
The ACMD is a statutory body which was established by Parliament after the important 1971 Act which fundamentally changed the landscape of probation in the UK.
The act brought in the concept of classifying illegal drugs into three categories, Class A being the most harmful.
He was named chair designate in May 2008 and took over the post in November. He was due to stay in the post until 2011.
His duties include making scientific recommendations to ministers on how to classify banned drugs, based on the harm they can cause.
And it is Prof Nutt's analysis of the harms posed by cannabis, other risks in society, and his frustration with ministers' positions, which have caused his downfall.
Two controversies in particular led to his sacking by the Home Secretary Alan Johnson.
Jacqui Smith: Furious with the professor
In January 2009, Prof Nutt wrote an article in a scientific journal, debating how society assesses various risks.
The paper was headlined "Equasy, an over-looked addiction with implications for the current debate on drug harms".
He said the point of the article was to explain that the harm from illegal drugs could be equal to harm in other parts of life, such as horse-riding, hence the invented term equasy or "equine addiction syndrome".
Prof Nutt argued that "equasy" could be blame for 10 deaths a year and more than 100 traffic accidents.
Asked to clarify what he meant, he told the Daily Telegraph that there was "not much difference" between the harm caused by riding and ecstasy. Society, he argued, did not always "adequately balance" all of the risks inherent in it.
"Making riding illegal would completely prevent all these harms and would be, in practice, very easy to do.
"This attitude raises the critical question of why society tolerates - indeed encourages - certain forms of potentially harmful behaviour but not others, such as drug use."
Perhaps predictably, the article sparked fury from anti-drugs campaigners who accused him of going on a personal crusade to downgrade the drug from Class A to B.
Demand for apology
The then Home Secretary Jacqui Smith ordered Prof Nutt to apologise, accusing him of trivialising the dangers of the drug. She said he had gone beyond his role as the chairman of the ACMD, although he argued that he was writing in his professional capacity and trying to add to important debates.
Weeks later, the ACMD recommended the downgrading - but ministers had already made clear that wasn't going to happen.
Professor Nutt stuck to his guns and in the summer gave a lecture on the relative risks of various drugs which, in turn, became a paper published by one of the UK's leading university departments of criminology.
In the paper, he reproduced a chart of drugs and other substances, based on their risk to health. The chart stated that alcohol and tobacco were more harmful than many illegal drugs, including LSD, ecstasy and cannabis.
But he then went beyond that and criticised the moral tone of policy decisions.
Prof Nutt argued that Jacqui Smith's "precautionary principle" of erring on the side of caution, particularly by reversing a decision to downgrade the classification of cannabis, could do more harm than good.
Moving a drug up the classification scale could give it greater cachet and increase the likelihood of people seeking it out, he said.
"I think the precautionary principle misleads," he wrote. "It starts to distort the value of evidence and therefore I think it could, and probably does, devalue evidence.
"This leads us to a position where people really don't know what the evidence is. They see the classification, they hear about evidence and they get mixed messages."
That was the final straw for Ms Smith's successor. Mr Johnson said that Prof Nutt had gone beyond his remit and, by lobbying for a change in government policy, had undermined the government's attempts to provide clear messages on drugs.
Prof Nutt has not left the post quietly. His parting shot accused ministers of undermining scientists and their work in providing evidence to inform policy.
His supporters will say that the government has sacked a top scientific adviser doing his job and using science.
But his critics will say that he should have thought a little bit more about the realities of drugs policy and society.