Labour's George Galloway, who has campaigned against air strikes on Iraq, named four people he alleged were agents of Mossad, the Israeli secret service, working under false names and papers with the Unscom team.

But Foreign Secretary Robin Cook said he had "no corroboration" of the claims, which he said emanated from Baghdad.

Richard Butler: "A congenital liar" according to Mr Galloway's sources

Mr Galloway also said a senior UN official had told him that Unscom head Richard Butler was "a congenital liar" - an allegation "utterly" rejected by Mr Cook.

The clash came in Commons exchanges after the Foreign Secretary made a statement on the deepening crisis over Iraq's withdrawal of co-operation with the UN weapons inspectors.

Unscom's former chief of inspectors, Scott Ritter, has alleged the organisation received substantial aid from Mossad.

Mr Galloway demanded: "Isn't the problem the total bankruptcy of Unscom as a credible player in this whole affair?

'Working under pseudonyms'

"Recently a very senior official of the UN described to me Richard Butler, the head of Unscom, as a congenital liar - and this on the basis of decades of knowledge of the man."

He said: "Scott Ritter since his resignation had admitted that he was working with Israeli intelligence whilst being the deputy head of a UN mission in Baghdad."

The Glasgow Kelvin MP went on: "In the last few hours it has been revealed that four inspectors working in Iraq under pseudonyms and carrying false passports were in fact Colonel Khadouri, Lieutenant Shamani, Colonel Rabscon and Jador Dalal Shamoni - all operatives of the Mossad Israeli intelligence."

Mr Galloway added: "All of us hope that these inspectors can get back to work monitoring these awful weapons, which exist not only in Iraq but throughout the region, not least in Israel.

Scott Ritter: Resigned

"But a new and credible leadership of Unscom, and transparency in its work, will be required as a precondition for credibility to be restored."

He demanded a timescale for the ending of sanctions against Iraq, which he said were killing 6,000 Iraqi children each month.

Replying, Mr Cook said: "I have heard of the reports that there have been four people alleged by Baghdad to be working for Israel within Unscom.

"I have to say to the house at the present time that I have no corroboration of these reports - and they do stem from Baghdad."

He told Mr Galloway: "I have to say in respect of Mr Butler that I strongly disagree with his characterisation.

"I have known Richard Butler long before he became the head of Unscom. I am bound to say I know him to be a committed diplomat.

"I would utterly acquit him of the charges made against him."

Mr Cook added: "Baghdad's main complaint against Richard Butler is that simply he has been too robust in carrying out the job that the UN asked him to do."