As he emerged triumphant from his showdown with the Senate committee on Tuesday, George Galloway told reporters: “I'm a politician that pleads guilty to using events like these for political purposes.”

By most reckoning the British MP, an outspoken leftwinger who has campaigned in the UK against Iraq's occupation, stole the show.

The hearing, chaired by Republican Norm Coleman, had been presented as an opportunity for the committee to interrogate Mr Galloway over his alleged involvement in Iraq's oil-for-food programme and his alleged support for Saddam Hussein. The investigators had even offered to send airline tickets to ensure his attendance.

But in the event it was Mr Galloway who was on the offensive and it was Mr Coleman's credibility that was called into question.

Alternating between detailed rebuttal and sweeping denunciation, the MP derided the quality of the committee's evidence, his accusers' motives, and US policy in Iraq as a whole.

He did not deny that Fawaz Zureikat, his colleague and the man alleged to be the go-between for his oil allocations, could have been involved in the oil trade, saying instead that he had always known he was involved in Iraqi business.

Neither did he have a ready explanation for Iraqi letters, provided by the committee, that referred to oil deals with Middle East ASI, Mr Zureikat's company, next to Mr Galloway's name in brackets. He merely said he had not seen the documents before, and raised the possibility they might be forgeries.

Mr Galloway was adamant he had not met Mr Hussein many times, as claimed, but “twice”: the same number of times as Donald Rumsfeld, US defence secretary. He had long opposed Mr Hussein's dictatorship, even when “British and American governments and businessmen were selling him guns and gas”.

He owned no company that could have made profits from trading Iraqi oil, and he cast doubt on the reliability of evidence given by Iraqi officials now held prisoner by the US. He derided the committee's references to a libel case with The Daily Telegraph, a UK newspaper, as a “schoolboy howler”.

Mr Galloway also dismissed allegations that he was involved in paying bribes totalling hundreds of thousands of dollars to Mr Hussein as “utterly preposterous”.

And on the central contention that Iraq had allocated him oil through two front companies Aredio Petroleum or Middle East ASI Mr Galloway had a simple question: “Where's the money?” To that the committee had no answer.

Mr Coleman appeared a little lost for words. Carl Levin, the ranking Democrat on the committee, was quicker to rein in Mr Galloway's rhetoric, but even he struggled to silence the Scot's acerbic tongue.

But after the hearing Mr Coleman regained his voice, taking Mr Galloway on in the same terms. “Mr Galloway's credibility is certainly very suspect,” he said, and he warned there would be consequences if the MP could be shown to have lied under oath.

The documentation, the senator insisted, was consistent with other cases where there was clearer evidence. As Mr Coleman stressed, the committee was “not a court of law”. Both US federal and UN investigations still have some way to go.