The Government's chief scientific adviser is being aggressively targeted by American lobbyists trying to discredit his view that man-made pollution is behind global warming. In an interview with The Independent, Sir David King said he was being followed around the world by people in the pay of vested-interest groups that want to cast doubt on the science of climate change.

Last year, Sir David said the threat from global warming was greater than that posed by international terrorism and he has criticised the Bush administration for pulling out of the Kyoto treaty to limit greenhouse gas emissions.

Since then, he has given many lectures to international audiences but found individuals among them who are there solely to create the impression that he is presenting biased information.

"They'll be in the audience to stand up and raise questions to get into the audience's mind that I haven't represented a balanced view," he said.

"You have a group of lobbyists, some of whom are chasing me around the planet, which I'm chuffed about because it means they are worrying about what I'm saying, and these lobbyists stand up after I've given an hour's talk and say, 'There are scientists who disagree with you'," Sir David said.

"I always say, 'Which bit of the science that I've just presented to you are you challenging'? I don't get the answer."

Last November, Myron Ebell, from a right-wing Washington think-tank called the Competitive Enterprise Institute, said on BBC Radio 4 that Sir David is an "alarmist with ridiculous views who knows nothing about climate change".