Home Secretary Alan Johnson said today he had "lost confidence" in Professor David Nutt's ability to be his principal adviser on drugs policy.
Answering an emergency question in the Commons, Mr Johnson said he asked Prof Nutt to resign because his role was "to advise rather than criticise Government policy".
But he insisted his dismissal was "not a reflection" on the work of the Advisory Council on the Misuse of Drugs (ACMD) and he would be meeting other members "shortly".
Two members of the ACMD have already quit after the sacking of Prof Nutt and others are threatening to follow.
To Tory cheers, shadow home secretary Chris Grayling said the Home Secretary's decision on Friday was "the right one".
Mr Johnson said the advisory committee's work had been "invaluable" to successive governments.
Of the 21 recommendations made by the committee on cannabis policy last year, the Home Office accepted 20 and rejected just one, on classification.
A later report on ecstacy included 13 recommendations, of which the Home Office accepted 11.
"I asked Prof Nutt to resign as my principal drugs adviser not because of the work of the council but because of his failure to recognise that as chair of ACMD his role is to advise rather than criticise Government policy on drugs."
Mr Johnson recalled that in February, while awaiting publication of the Government's position on the classification of ecstacy, Prof Nutt published an article and "addressed the media on the appropriateness, or otherwise, of the Government's policy framework, expressing a view that horse riding was more dangerous than ecstacy.
"On Thursday October 29 Prof Nutt chose, without prior notification to my department, to initiate a debate on drugs policy in the national media, returning to the February decisions, and accusing my predecessor or distorting and devaluing scientific research.
"As a result, I have lost confidence in Prof Nutt's ability to be my principal adviser on drugs."
Mr Johnson said the advice of independent scientific advisers was essential to the Government.
"The role of such advisers is to provide independent advice to government based on their professional scientific expertise.
"The role of government is to consider that advice carefully, along with all other relevant factors, and for this House to endorse or reject those decisions, where appropriate."
Mr Grayling said independent advice was important. "But those who take on formal roles, with government, have to be extremely cautious about the things they say.
"Prof Nutt's comments earlier this year comparing the risks of ecstasy with horse riding were, I thought, particularly ill-judged."Reuse content