The government's chief scientific adviser says he will not be "muzzled" despite being told by Downing Street to limit his media interviews.
King says he was quoted in numerous US newspapers
The No 10 memo came after Sir David King said climate change was a bigger problem than the threat of terrorism.
On Tuesday, Sir David appeared on BBC Radio 4's Today programme - the show he was advised to avoid.
He said advice on conveying a message was helpful but people had to know scientists would speak their minds.
Blair official's warning
In January, Sir David wrote an article for the American journal Science criticising the US Government for failing to take global warming more seriously.
"In my view, climate change is the most severe problem we are facing today, more serious even than the threat of terrorism."
The Independent newspaper on Monday published a leaked memo sent to Sir David in February by the prime minister's principal private secretary, Ivan Rogers.
It advised the scientist to decline any interview requests from British and US newspapers or the Today programme.
"To accept such bids runs the risk of turning the debate into a sterile argument about whether or not climate change is a greater risk," said Mr Rogers.
"This sort of discussion does not help us achieve our wider policy aims ahead of our G8 presidency next year."
Sir David said he had seen the memo and the newspaper report but pointed to the "numerous" interviews he had given on a recent trip to America.
Asked about the memo, he told Today: "I am saying this is not the way that things worked out. Throughout my trip the whole idea was to get the public aware of the British leadership position on the issue of climate change."
His mantra was openness, honesty and transparency, he said.
"I don't believe we can keep the public on side if it's not understood by the public that our scientists are prepared to go out and say what they mean," he argued.
Sir David said advice from professionals about how to get across a message was helpful, but it did not mean his answers coincided with that advice.
The Independent reported that the scientist had been given a list of 136 mock questions which reporters might ask, along with suggested answers.
One question said: "How do the number of deaths caused by climate change and terrorism compare?"
The suggested answer was: "The value of any comparison would be highly questionable."
Sir David told Today he was working on both climate change and terrorism issues and his assessment, expressed in the journal article, had not changed.