When a scientist who happens to be the Government's top adviser on drugs policy says that horse-riding appears to be more dangerous than taking ecstasy, you would think that his words might be met with curiosity, instead of hostility and outrage.

Similarly, when criminologists have stacks of evidence showing that large-scale imprisonment has little effect on crime levels and can even make things worse, how is it that we have the biggest prison population ever?

Why is no one listening to those collecting the evidence on which the Government has claimed its policies would be based?

It is a sensible idea: base decisions on facts and the latest findings instead of prejudice and dogma. But policymakers want certainty, and, unfortunately, different researchers can reach different conclusions that are littered with qualifications and caveats.

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One analysis put academics last on the list of those who senior officials turn to for evidence, below consumers, with special advisers and so-called experts at the top. And to policymakers, research findings are not the last word in evidence, which can take many forms, all of which compete for attention.

When the Advisory Council on the Misuse of Drugs - the independent expert body headed by David Nutt, the scientist who caused the recent furore - recommended that ecstasy be downgraded, its recommendation was rejected in favour of a view fashioned by newspaper commentators and political expediency.

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Professor Nutt rightly accused ministers of being swayed by "politics" rather than scientific evidence. "Our job is not to give messages to the public. Our job is to tell the Home Secretary and Drugs Minister about the relative harms of drugs," he told the BBC.

Sir David King, the former Chief Scientific Adviser, knows at first hand how science can struggle to be heard: "If you are a scientist, (it is a case of) get back in your box. We will lift the lid when we want the message."

And that appears to be the crux of the matter: researchers do not always tell ministers what they want to hear. But that is the very point of academic evidence. It is independent, and thus free from interference and vested interests. Ministers can reject it, but if they do they should do so without pandering to an ill-informed public and to opinion polls.

The Government's stance on both ecstasy and cannabis policy has left one eminent neuroscientist incredulous. Colin Blakemore questions ministers' commitment to evidence-based policy when they are so keen to listen to an irrational media and to reflexively offer populist solutions.

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Newspaper columnists are there to proffer opinions, to trot out the very hobby horses that a thoughtful and rational Government should resist. But that is not evidence. It is not peer-reviewed for publication, so why should it be given more credence than the independent research of an academic? Take this commentary on the Nutt ecstasy episode: "Horse-riding is not inherently harmful. Drug-taking is. Horse-riding is not addictive. Drug-taking is. Most people who ride horses do not come to any harm. The only reason there are not many more deaths from ecstasy is that, unlike horse-riding, it is illegal."

Perhaps the Government should remember that riding hobby horses can be a dangerous pastime, too.