Sir David King was seen as someone who spoke his mind.
The UK's chief drugs adviser has been sacked by the home secretary after criticising official policy. But what exactly is the role of a government adviser?
Alan Johnson has said he "lost confidence" in Prof David Nutt, head of the Advisory Council on the Misuse of Drugs, following his criticism of the government's decision to reclassify cannabis to Class B from C.
Sir David King, the UK's Chief Scientific Adviser between 2000 and 2007, was seen as someone who spoke his mind. In 2004, for example, he berated the US for failing to tackle greenhouse gas emissions.
But he told the BBC there was a fine line to be drawn in the role.
Speaking on Radio 4's The World Tonight, Sir David said he thought it wrong for a scientific adviser to openly criticise a public statement by a minister.
"When I was in government I did make it very clear to people in government that whatever advice I gave to ministers, I would eventually put into the public domain and I would put it in the clearest possible way," he said.
"And my reason for that, quite simply, was that any science adviser within government needs to maintain the trust of the public. But this is a fine line, because in addition, you have to maintain the trust of ministers and the prime minister."
Sir David said Prof Nutt "stepped over the line is by being overtly critical" of the home secretary, Jacqui Smith.
"A political decision was made, going beyond the scientific advice," Sir David said.
"But that is precisely what the politicians are for. The politicians have to take everything else into account."
When he was an adviser, Sir David said, he understood it was not legitimate to openly criticise decisions made by ministers. Nonetheless, there were no written rules stating that he could not.
His 2003 advice that new nuclear power stations were needed to manage climate change problem was not followed.
He said: "I still made my advice clear in the public domain, but did not criticise the government for not following it."
As a civil servant, government advisers are in "an unusual position of having a public voice at all", he said.
"Very often politicians want to put the 'white coats' to the media because we were the guys who could manage the difficult questions they would throw at us."
But it was not an equal partnership - because politicians are able to openly distance themselves from their advisers.
"The time I spent in government... I don't think there was a time when they specifically attacked the science," he said. They would say 'this time we're not going with the scientific advice, for the following additional reasons'."
However, according to one current government adviser, "Scientific data and their independent interpretation underpin evidence-based policy making - and nobody rational could possibly want a Government based on any other type of policy making."
Prof Chris Higgins, chair of the Spongiform Encephalopathy Advisory Committee, told the Science Media Centre: "It is critical that Chairs and members of independent scientific committees are not just independent of Government but are positively encouraged to provide the best possible interpretation of the available scientific data, whether or not that interpretation 'fits' with the current political view."