Reefer madness

I had always thought of Alan Johnson, the Home Secretary, as a safe pair of hands. After seeing him expostulate on David Nutt, "safe" is no longer my adjective of choice. Senior representatives of the scientific community including Lord Drayson, the Science Minister, John Beddington, the Chief Scientific Adviser, and Lord Rees, president of the Royal Society, have voiced their disapproval of his sacking of Professor Nutt.

Mr Johnson seems to have taken against Professor Nutt's Eve Saville Lecture at King's College London's Centre for Crime and Justice Studies, published on the university's website last month. I will come back to what Professor Nutt said, but first I want to comment on scientific advice and government in general.

This country has a strong record of providing and accepting scientific advice, with 75 independent scientific advisory committees covering a range of topics. Many of the experts on these committees are academics, who are delighted that their expertise is valued and that they can contribute to policymaking. The Government has repeatedly said that it is committed to evidence-based policy, and expert committees are a key part of this.

The process of providing advice nowadays is open and inclusive - a huge change from the past. I recall the late Sir Richard Southwood, emeritus professor of zoology at the University of Oxford, telling me that when his expert group was first established to look into bovine spongiform encephalopathy in the late 1980s, secrecy was imposed by ministers: he was not even supposed to acknowledge the committee's existence. Contrast this with today, when advisory committees - including the Advisory Council on the Misuse of Drugs (ACMD) from which Professor Nutt was sacked - hold meetings in public and put their minutes on the web. But how does scientific advice link to policy?

No one expects there to be a linear flow from science to policy, because policy has to weave in a range of factors such as affordability, acceptability and enforceability. One way of expressing this is to say that science assesses risk while policy manages it. Nevertheless, ministers often turn to the experts for a strong steer on policy. For example, the expert group I created for the 2001 foot-and-mouth epidemic drove policy on control of the disease.

I cannot think of any instance I have been involved with in which scientific advice was rejected. So what went wrong with cannabis? The ACMD's 2008 report on the drug is clear and careful. Sir Michael Rawlins, then chair, in his letter to the former Home Secretary Jacqui Smith, says cannabis is a "significant public health issue", but that after careful scrutiny, "the majority of the council's members consider - based on its harmfulness to individuals and society - that (it) should remain a class C substance".

Professor Nutt, in his lecture, reviewed the ACMD's conclusions and stated that the Government's reasons for rejecting them were based on public perception and the precautionary principle. On the former, the data are by no means clear cut: the ACMD's own MORI poll in 2008 shows that while members of the public tend to think that cannabis should be classified as A or B, they believe the penalty should be no higher than that of a class C drug (suggesting that the classification system is not well understood, since it defines the penalties associated with possession and trading). The precautionary principle, Professor Nutt argued, can mean all things to all people and is not a robust reason for rejecting considered advice.

To sack a distinguished scientist for giving a thoughtful lecture commenting on the relationship between scientific advice and policy is an appalling misjudgment. On this basis, as chair of the Food Standards Agency, I should have been sacked a dozen times. There is a risk that the Nutt affair could undermine scientists' confidence in the advisory system. This is why I supported the statement of principles sent to the Prime Minister on 5 November, asking the Government to reaffirm its commitment to academic freedom and independence, and the proper consideration and explanation of its response to advice.