For climate sceptics it was a key piece of evidence showing that the scientists behind global warming could not be trusted. A quotation by one of the world's most eminent climate scientists was supposed to demonstrate the depths to which he and his ilk would stoop to create scare stories exaggerating the threat of global warming.

Sir John Houghton, who played a critical role in establishing the Intergovernmental Panel on Climate Change (IPPC), was roundly condemned after it emerged that he was an apparent advocate of scary propaganda to frighten the public into believing the dangers of global warming.

"Unless we announce disasters, no one will listen," Sir John was supposed to have said in 1994.

The quotation has since become the iconic smoking gun of the climate sceptic community. The words are the very first to appear in the "manual" of climate denialism written by the journalist and arch-sceptic Christopher Booker. They get more than a 100,000 hits on Google, and are wheeled out almost every time a climate sceptic has a point to make, the last occasion being in a Sunday newspaper article last weekend written by the social anthropologist and climate sceptic Benny Peiser.

The trouble is, Sir John Houghton has never said what he is quoted as saying. The words do not appear in his own book on global warming, first published in 1994, despite statements to the contrary. In fact, he denies emphatically that he ever said it at any time, either verbally or in writing.

In fact, his view on the matter of generating scare stories to publicise climate change is quite the opposite. "There are those who will say 'unless we announce disasters, no one will listen', but I'm not one of them," Sir John told The Independent.

"It's not the sort of thing I would ever say. It's quite the opposite of what I think and it pains me to see this quote being used repeatedly in this way. I would never say we should hype up the risk of climate disasters in order to get noticed," he said.

Even though the quotation appears on about 130 thousand web pages, no one seems to know where it originated. On the few occasions a reference is cited, it is listed as coming from the first edition of Sir John's book, Global Warming: The Complete Briefing, published by Lion Books in 1994. But Sir John does not say it in this edition, nor in subsequent editions published by Cambridge University Press.

Christopher Booker, a newspaper columnist, considers the quotation so important that he lists it at the top of the first page of his most recent book on climate scepticism, The Real Global Warming Disaster, published last year. Mr Booker also cites the 1994 edition of Houghton's own book on global warming as the source of the quotation, even though there is no mention of it there. Mr Booker did not respond yesterday to enquiries by The Independent.

Benny Peiser, a social anthropologist at Liverpool John Moores University, also cited the 1994 edition of Sir John's book as the source of the quote, which he used last Sunday in an article denouncing the alarmism of climate scientists. Dr Peiser admitted to The Independent that he had not read the book recently and had only used the quote "from memory" because it is so widely cited in other books on climate scepticism.

"I've seen it printed in many books. He is well known for making these statements. I've used that quote on many occasions from one of the books on climate alarmism. If he makes the claim that he never said this then he has to clarify that," Dr Peiser said.

"If he publicly says that he never made that statement then, of course, I wouldn't use it, but this is the first time I've heard [his denial] and this has been going on for 15 years. This quote has been used for the past 15 years," he said.

In fact, the earliest record of the quote comes not from 15 years ago but from November 2006 when it appeared in a newspaper column written by the journalist Piers Akerman in the Australian newspaper The Sunday Telegraph. Akerman, a controversial right-wing columnist and global warming sceptic, appears to be the first person to use the quote verbatim in an opinion piece criticising the Stern Review, which looked at the economic effects of global warming.

"This alarmist approach reeked of stupidity, snake oil, and misguided gospel preaching but was in line with a formula adopted by the first chairman of the IPCC, Sir John Houghton, who produced the IPCC's first three reports in 1990, 1995 and 2001 and wrote in his book Global Warming, The Complete Briefing, in 1994: 'Unless we announce disasters no one will listen'," Mr Akerman said.

Within three years of Akerman's piece being published, climate sceptics had jumped on the supposed quotation, citing the source as Houghton's 1994 book. Mr Akerman said that he could not remember where the quote came from but he will check his records.

Christopher Monckton, 3rd Viscount Monckton of Brenchley, also cites the 1994 book as the source of the quote, which he uses extensively in his writings and lectures advocating climate scepticism. The quotation, he says, is a prime example of the alarmism and exaggeration of the climate change community and the IPCC.

Although Lord Monckton replied to an email asking him for the source of the quotation, he did not reply to a second email pointing out that it does not appear anywhere in Houghton's 1994 book.

Sir John, who was the former head of the Met Office but is now living in semi-active retirement in Wales, said he is considering taking legal action because he feels that the continued recycling of the misquotation is doing him and his science a huge disfavour.

"It doesn't do me any good because it suggests to everyone that I have hyped things up. I've been growing aware of it now for some time. The trouble is, if I just deny it then it cuts no ice with the people who want to believe it. I have to consider legal action," Sir John said.

How Sir John's words were twisted

The scientist...

Sir John Houghton

He is one of the most distinguished climate scientists of his generation. He was professor of atmospheric physics at Oxford University until 1983, when he became director general of the Meteorological Office where he established the Hadley Centre. A devout Christian, Sir John has been a strong advocate of the global research effort into climate change. He was the first head of the scientific working group of the Intergovernmental Panel on Climate Change (IPCC) and was lead editor of the panel's first three reports outlining the science of global warming. In 1994 he popularised the message of these reports in a book called Global Warming, The Complete Briefing. The book is widely cited by climate sceptics as saying: "Unless we announce disasters, no one will listen". However, Sir John said that this quote does not exist anywhere in the book and he has never said or written such a statement.

... and the sceptics

Lord Monckton

Otherwise known as Christopher Monckton, he is one of the most articulate and theatrical of the climate sceptics, lecturing extensively in the US. He likes to identify errors by climate scientists which he says fall in the direction of "undue alarmism and flagrant exaggeration". He has frequently cited the quotation of Sir John Houghton's as a prime example of the deeply flawed nature of the scientists behind the global warming "scare". Lord Monckton cited the source of the quote as Sir John's 1994 book, but did not reply to enquiries pointing out his error.

Christopher Booker

A journalist and author, Booker has been a thorn in the side of climate scientists. His latest book, The Real Global Warming Disaster, is seen as the "manual" of climate scepticism. He deems Sir John Houghton's quote as being so important that it lies at the top of page one. Again, the source of the quote is cited as the 1994 edition of Sir John's book on global warming. Booker has been a fierce critic of the IPCC and of Sir John's Hadley Centre. He believes that the computer models used by climate scientists are deeply flawed and that it is not carbon dioxide that has been driving the climate but natural changes driven by the activity of the Sun and changes to the ocean currents. In short, Booker believes that global warming is merely a "bizarre set of collective delusions".

Benny Peiser

A social anthropologist at Liverpool John Moores University, he has not published any scientific research into climate change, but believes that the field is marred by alarmism. He has also used the Houghton quotation, but said yesterday that he cannot recall where he had come across the quote, except that it was from another book on climate alarmism. Peiser said he was unaware that Sir John denies saying the words.

Roger Helmer