Government divisons over the sacking of its chief drug adviser deepened yesterday as its most senior scientist backed Professor David Nutt for saying that cannabis was less harmful than alcohol.

Professor John Beddington, the Chief Scientific Adviser, said research showing the drug to be less dangerous than alcohol and cigarettes was “absolutely clear cut”, though he stopped short of criticising Alan Johnson’s decision to dismiss him.

Professor Beddington’s intervention came as it emerged that Lord Drayson, the Science and Innovation Minister, e-mailed No 10 at the weekend to say that he was “pretty appalled” by the Home Secretary’s move, which had the scientific community “up in arms”.

Both were abroad when Professor Nutt was dismissed — Lord Drayson in Japan and Professor Beddington in Russia — and neither was consulted by Mr Johnson despite their roles in overseeing science advice across Whitehall.

Lord Drayson wrote in an e-mail to Nick Butler, the Prime Minister’s policy adviser: “Alan did this without letting me know and giving me a chance to persuade him it’s a big mistake. Is Gordon able to get Alan to undo this? As ‘science champion in Government’, I can’t just stand aside on this one.”

He later issued a statement saying that this was an “immediate reaction to what had happened without full knowledge of the facts” and that Mr Johnson had since assured him of his respect for scientific advice.

Professor Beddington told the BBC that he accepted that there was a difference between scientific advice and ministerial decision-making, and that Mr Johnson had been placed in a difficult position by Professor Nutt’s criticism of the reclassification of cannabis as a Class B drug.

“I think it’s very difficult — when clearly trust had broken down between the Home Secretary and Professor Nutt — to see how that could go on,” he said.

Asked whether he agreed with Professor Nutt that cannabis was less harmful than cigarettes and alcohol, he said: “I think the scientific evidence is absolutely clear cut. I would agree with it.”

He said that he would consult heads of other expert committees to ask whether they had experienced difficulties.

Professor Beddington has previously been critical of the Home Office’s attitude to scientific advice. He wrote to Jacqui Smith, then Home Secretary, in January expressing concern that she appeared to have pre-empted a report from the Advisory Council on the Misuse of Drugs (ACMD) on the classification of Ecstasy. He told Ms Smith in March that her public criticism of Professor Nutt risked discouraging scientists from working with the Government.

Evan Harris, the Liberal Democrat science spokesman, said: “The revelation of Lord Drayson’s e-mails, and the support for David Nutt from the government Chief Scientific Adviser, shows that the Home Secretary’s position is unsustainable.

“It is time for Alan Johnson to recognise that he blundered over his decision, and the manner of it, because the Government is facing a deepening crisis of confidence from the scientific community.”

Mr Johnson was backed by the Prime Minister, who said: “I think Alan Johnson made the right decision because we cannot send mixed messages. Advisers advise and ministers have to make decisions.”

Fresh evidence supporting Professor Nutt’s view that cannabis is less harmful than alcohol or cigarettes has also emerged from new research led by one of his former colleagues on the ACMD.

Matthew Hickman, Reader in Public Health and Epidemiology at the University of Bristol, has found that thousands of young people would have to stop smoking the drug heavily to prevent even a single case of schizophrenia or psychosis — the Government’s main justification for reclassifying it as a Class B drug.

“The likely impact of reclassifying cannabis in the UK on schizophrenia or psychosis incidence is very uncertain,” Dr Hickman said.

In a study published in the journal Addiction, Dr Hickman’s team examined the evidence for a link between cannabis and psychosis, the background risk of psychosis among different age groups and sexes, and the numbers of cannabis smokers in the UK.

It found that while there was evidence to suggest that heavy cannabis smokers might have twice the normal risk of developing psychosis, the reclassification of cannabis would have to have a very large deterrent effect to greatly influence public health.

To prevent one case of psychosis, it would be necessary to stop at least 2,800 men aged 20 to 24 from smoking the drug heavily, or 4,700 men aged 35 to 39. For women, it would be necessary to dissuade at least 5,470 smokers in the younger age group, or at least 10,870 in the older one.

For light cannabis use, a single case of psychosis would be prevented only if more than 10,000 young men or nearly 30,000 young women were to stop smoking the drug.

Dr Hickman would not comment on Professor Nutt’s sacking, though he is understood to be among the ACMD members who have written to Mr Johnson to express their concerns. Instead, he referred The Times to a statement he made about the addiction paper.

“Preventing cannabis use is important for many reasons — including reducing tobacco and drug dependence and improving school performance,” Dr Hickman’s statement said. “But our evidence suggests that focusing on schizophrenia may have been misguided.

“Our research cannot resolve the question whether cannabis causes schizophrenia but does show that many people need to give up cannabis in order to have an impact on the number of people with schizophrenia. The likely impact of reclassifying cannabis in the UK on schizophrenia or psychosis incidence is very uncertain.”

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