By Andrew Grice, Political Editor
Alan Johnson failed in an attempt to defuse the damaging row between the Government and Britain's top scientists after three more of his drugs advisers resigned last night.
The Home Secretary suffered a setback when another three members of the Advisory Council on the Misuse of Drugs resigned despite his efforts to reassure them in more than an hour of peace talks that the Government would respect the independence of its expert advisers.
The growing rift between ministers and the scientific community was sparked by Mr Johnson's decision to sack the body's chairman, Professor David Nutt, for allegedly campaigning against the Government's decision to upgrade cannabis to a Class B drug.
Another two members of the 31-strong council, Marion Walker and Dr Les King, resigned in protest and they were joined by three more members last night, leaving the group without experts in key areas of expertise. Chemist Dr Simon Campbell, psychologist Dr John Marsden and scientific consultant Ian Ragan quit after arguing unsuccessfully for Professor Nutt to be reinstated.
Allies of Mr Johnson said they were saddened by the resignations but insisted the Council was still viable and that most of its members wanted to carry on their vital work.
It is believed the Council was divided after yesterday's tense session with Mr Johnson. Some members wanted to accept his safeguards over their future work but others remained unhappy, accusing the Government of prejudging the review of cannabis ordered by Gordon Brown when he became Prime Minister. The drug was upgraded from Class C to B last year even though the Council opposed the move.
The Home Secretary promised his drug advisers yesterday that their views will be given "due weight" in future and acknowledged the need to improve relations with the Council. But he stood by his decision to dismiss Professor Nutt.
"I understand why the Advisory Council on the Misuse of Drugs was concerned about this, said Mr Johnson. "Its major concern was because they felt Professor Nutt was being dismissed for his views. I reassured them that was not the case."
He added: "There is a duty I think to accept that politicians make the final decision. At my meeting we talked constructively about the future, about what we can do to reassure the science community that their decisions are important to us and they are given due weight."
Evan Harris, the Liberal Democrats' science spokesman, said: "The latest resignations represent a deepening in the crisis of confidence of scientists in the Government – in particular in the Home Secretary. That they come after Alan Johnson met the ACMD demonstrates that he just doesn't get it when it comes to the importance of respecting the academic freedom and integrity of independent, unpaid science advisers."
Mr Johnson said a joint code between government and scientists, proposed by the Royal Society, was being considered by Mr Brown and the Government's chief scientific adviser. In a joint statement released by the Home Office, the meeting was described as "very constructive".
It said: "The Home Secretary emphasised the value he placed on ACMD's advice, the important contribution the ACMD had made to government drugs policy in the past and how he expected it to continue do so in the future."
In the wake of the sacking of Professor David Nutt as chairman of the United Kingdom's Advisory Council on the Misuse of Drugs (ACMD) by Home Secretary Alan Johnson and the subsequent resignations of Dr Les King and Marion Walter, three more scientists have now resigned. This follows a meeting on Monday between the Council and Alan Johnson, at which the Council sought reassurances that the integrity of the Council would not be compromised. Prior to the meeting, the Council sent a letter to Mr Johnson to the effect that a majority of its membership was deeply concerned about the circumstances relating to and surrounding Professor Nutt's dismissal: "For some members, these matters are of such seriousness as to raise the question whether they can, in good conscience, continue on the Council."
Alan Johnson, the politician at the centre of the row, taken in 2007 
The scientists in question are the chemist, Dr Simon Campbell,  a psychologist, Dr John Marsden and a pharmaceutical consultant, Ian Raglan. 

Commenting on his resignation on BBC Radio 4's Today programme, Dr Campbell said "I do not accept the reasons given for Professor Nutt's dismissal, I think that was a clash of personalities. I do not agree with the manner in which he was dismissed. Such an abrupt dismissal was a humiliation for such a respected scientist." 

These resignations means that the ACMD is no longer constitutionally able to function and that six positions will need to be filled. There is a possibility that further resignations may occur as a number of the remaining members of the Council are reported to be unhappy with the prevailing situation, although many of those who do remain sit in the capacity of representatives of organisations with an interest.