This Government is fond of promoting its decisions as “evidence-based policy”, grounded in the findings of research. Civil servants and scientists, however, like to joke that what it really values is something rather different: policy-based evidence that justifies a course of action that has been decided on for political reasons.

Ministers, of course, are perfectly entitled to do this. They are democratically elected; expert advisers are not. While scientists might prefer politicians to do as they are told, their view is often just one of many factors to consider.

Few scientists who advise the Government are naive enough to expect that their opinions will never be overruled, but if this is to happen they rightly expect certain behaviour in return. They should be consulted in good faith before a decision has been made. Their advice should be clearly communicated to the public, along with an explanation of why it has not been taken. And they should not be admonished or silenced if their views are not politically convenient.

In the David Nutt affair, the Government has failed on all counts. The Advisory Council on the Misuse of Drugs was asked to review cannabis after the Prime Minister had made his intention to toughen its classification clear. Its findings were then released through the Home Office press office, which briefed journalists negatively. Professor Nutt’s dismissal has now provided the final insult.

This saga could certainly deter experts from advising the Government, not only in science but in other areas of public policy. We are not talking about ministers that are bound by collective responsibility, or Civil Service employees, but independent academics with a day job who often give their time and knowledge for free. They have a right to speak plainly, without being spun against or sacked. There is no point in having expert advisers if they can say only what the Government wants to hear.

In highlighting so clearly how ministers ought not to behave, Alan Johnson may yet have performed a service to colleagues who value scientific advice more highly than he does. His spectacular own goal with the scientific community presents an opportunity to strengthen its voice in Whitehall.

Lord Drayson, the Science Minister, would do well to use it to press for two sensible proposals made recently by the Commons Science and Technology Select Committee that would help to prevent a repeat of this fiasco.

An independent media office serving all of the Government’s advisory panels would remedy the ridiculous situation where the Home Office was tasked with communicating scientific advice it was keen to undermine.

Departmental chief scientists, too, should be required to report and explain all instances where expert advice has been sought but not followed. Both measures would make ministers think twice before commissioning opinions they have no intention of heeding and then shooting the messenger.

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