By Barnaby Mason BBC diplomatic correspondent

In the past few weeks, the United States and Britain have put increasing emphasis on an alleged connection between the Iraqis and Osama Bin Laden's al-Qaeda network.

The document noted what many observers have drawn attention to: that the two are unlikely bedfellows

In his latest comment, the British Prime Minister, Tony Blair, told parliament in London that there were unquestionably links between al-Qaeda and Iraq.

Although just how far they went was a matter of speculation.

However, some doubt has been cast on these assertions by a British defence intelligence document leaked to the BBC.

'Unlikely bedfellows'

The document said: "While there has been contact between al-Qaeda and the Iraqi regime in the past, we believe that any fledgling relationship foundered due to mistrust and incompatible ideology."

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The document noted what many observers have drawn attention to: that the two are unlikely bedfellows.

Osama Bin Laden is - or was - a religious extremist who believes in the restoration of an Islamic caliphate to rule the Muslim world.

In his eyes, according to the document, the Baathist government in Baghdad is an apostate regime.

Others have described President Saddam Hussein as a secular fascist; however it may suit him sometimes to emphasise his Muslim credentials.

Unusually, the UK Government has in effect acknowledged the authenticity of the intelligence document.

Mr Blair said it was an internal paper from the Ministry of Defence; he had not been on the circulation list to see it.

His spokesman said you could not take a few lines from one piece of analysis and say that that represented the judgement of the British Government; you had to have access to the complete intelligence jigsaw.

On the other hand, the Foreign Secretary, Jack Straw, picked out one thing from the document to bolster the government's case - its conclusion that the training of some al-Qaeda members in Iraq might have continued.

Hardening the stance

Clearly the whole business of intelligence, of trying to make sense of a mass of often conflicting and sometimes unreliable information, is a matter of selection and difficult judgement.

Powell is out to prove Iraq cannot be trusted

Mr Straw denied a key charge: that the government was exaggerating or distorting intelligence for its own political purposes, and that some intelligence officers were dismayed at what was going on.

It is clear that the UK Government - and the Bush administration - would have an interest in any evidence that pointed to organisational or operational links between al-Qaeda and Saddam Hussein.

It is generally accepted that Osama Bin Laden's group was behind the 11 September attacks.

If Iraq could be tarred with the same brush, even indirectly, it would strengthen the justification for going to war.

Britain has been gradually hardening its statements on the subject, echoing Washington.

In public, ministers have chosen their words carefully. Officials have gone further.

Last week, the Foreign Office said there were al-Qaeda operatives in areas of Iraq where Saddam Hussein had full control - that is, not only in the Kurdish north.

It was hard to imagine they were there without the knowledge and acquiescence of the regime.

Now Mr Straw says there is a stream of intelligence showing that the regime is creating a permissive environment for terrorists including al-Qaeda to operate in.

'Counter-productive spin'

But he gives no specifics on al-Qaeda, referring instead to Iraqi support for what he calls Palestinian terrorist organisations and an Iraqi terrorist group operating inside Iran.

There must be a temptation for London and Washington to exaggerate intelligence that fits their view of Iraq. That is not to say they have given in to it.

But perceived exaggeration or spin would be counter-productive.

The danger is that people who are sceptical about the al-Qaeda link might be less inclined to believe the American and British case that Saddam Hussein is still concealing weapons of mass destruction.