The Ukip leader, Nigel Farage, has broken the consensus inside western intelligence by telling the BBC before his Europe debate with Nick Clegg that he believes the chemical attack in Syria last summer was conducted by the Syrian rebels, and not by the forces of the president, Bashar al-Assad.

Under continued pressure over his admiration for the Russian president, Vladimir Putin, Farage said: "I did admire what he had done over Syria. We were about to go to war in Syria because poison gas, sarin gas, had been used and everybody in London and Washington and Brussels assumed it had been used by Assad. And Putin said: 'Hang on a second, don't be so sure.' It turns out it is more than likely it was the rebels that used the gas. If Putin hadn't intervened we would now be at war in Syria."

He added: "I admire him as operator and head," adding that he was head and shoulders above Clegg.

His remarks are at odds with most expert opinion and the views of western intelligence. When he appeared on Russia Today in August Farage appeared to be more cautious in suggesting that the attack was by the rebels.

He was asked by his interviewer: "At this point there is no proof or any identification that the Assad government carried out the chemical attack, right?"

Farage replied: "What I'm saying is that I do myself believe that it's probable that they did but it's not absolutely certain. This whole situation is very, very complicated. And the so-called opposition are very split amongst themselves. And, probably, there are stronger hatreds between some of the opposition groups than there are against the Assad regime. We ought to be slightly cautious and we ought to absolutely make sure that it was Assad that used those weapons."

The US government has said it has "high confidence" that the chemical attack on Ghouta, near Damascus, on 21 August last year was carried out by Syrian government forces, a view backed up by monitored communications and on-the-ground analysis. The French government said the attack, using hundreds of kilograms of Sarin, could not have been carried out by anyone else.

UN investigators discovered several Soviet-made rockets which carried the chemical weapons in Ghouta. Human Rights Watch (HRW) said the rockets were fired from an Iranian-made launcher. Both rockets and launchers are used by the Syrian army and not normally used by rebels.

HRW also estimated that the rockets were fired from a military base on Mount Qassioun, which is home to the Syrian army's Republican Guards' 104th brigade.

Only the Syrian and Russian governments suggest that the Syrian government did not fire chemical weapons at Ghouta.