A Channel 4 documentary that claimed man-made climate change is a fraud broke strict broadcasting rules on impartiality, the media regulator said on Monday.

Ofcom said "The Great Global Warming Swindle" was unfair to several senior scientists and should have given a wider range of views on such a controversial issue.

However, the watchdog cleared the programme's makers of the serious charge of "materially misleading" viewers and said the first four of the programme's five parts did not breach impartiality rules.

The show, written and directed by film-maker Martin Durkin, was first shown in March 2007 and has been described as a response to Al Gore's Oscar-winning documentary "An Inconvenient Truth".

Durkin's film drew 265 complaints and provoked an intense debate on its central claim - that the human impact on global warming and climate change has been wildly overstated.

In the documentary the narration said: "Everywhere you are told that man-made climate change is proved beyond doubt. But you are being told lies.

"This is a story of how a theory about climate turned into a political ideology.it is the story of the distortion of a whole area of science."

The programme argued that there was "nothing unusual" about current temperatures.

Its approach was starkly at odds with the views of most mainstream scientists. Last month, U.N. Secretary-General Ban Ki-Moon said global warming was becoming the era's defining issue and would hurt rich and poor.

Many scientists predict rising seas, melting glaciers and more intense storms, droughts and floods as the planet warms.

Complainants said the programme was one-sided, misrepresented the facts, contained inaccuracies and distorted the science of climate modelling.

They also said it misled viewers by exaggerating the credentials of some contributors and leaving out key information.

Others complained that the show had unfairly promoted the idea that environmentalists seeking to reverse economic growth had pushed the theory of man-made global warming.

After the watchdog's ruling, Dave King, the government's former chief scientific adviser, said the link between human activity and climate change was "established beyond all reasonable doubt".

"Today, none but the most ill-informed can maintain that human induced climate change is not happening," he said in a statement. Channel 4 had no immediate comment.