Prime Minister's Question Time

Tony Blair will stand up in the House of Commons on Tuesday and attempt, yet again, to conclude the long debate about the invasion of Iraq. This may be the last chance for Mr Blair's critics to put the questions that still remain, even after four inquiries, about his decision to go to war. Raymond Whitaker reports

On 12 September 2002, the head of the Secret Intelligence Service, Sir Richard Dearlove, travelled from his post-modern headquarters at Vauxhall Cross on the south bank of the Thames, known derisively to MI5 across the river as "Legoland", to see Tony Blair at 10 Downing Street.

Sir Richard had a crucial piece of intelligence from a new source in Iraq which he wanted the Prime Minister to know about straight away. Downing Street, the intelligence services and half of Whitehall were working furiously to complete the Government's dossier on Saddam Hussein's presumed weapons of mass destruction, but there was disquiet among many of the experts about the lack of recent evidence.

Earlier that year an assessment from the Joint Intelligence Committee (JIC), the most important clearing-house for secret information, had lamented that intelligence on Iraq's WMD was "sporadic and patchy". As late as 21 August the JIC was saying: "We ... know little about Iraq's CBW [chemical and biological weapons] work since late 1998." That was when United Nations weapons inspectors, many of whom were reporting to Western intelligence, had been pulled out of Iraq.

But Sir Richard's service, more commonly known as MI6, had been making strenuous efforts to find out more, calling on all its sources in Iraq. One, a Baath Party member who had proved reliable on other subjects in the past, passed on information about CBW production and stocks, but stressed it was second-hand. Another said he had been told some battlefield munitions could be armed with CB agents in 20 to 45 minutes, but again could not vouch for the details himself.

This was enough for the JIC to "harden up" previous assessments that Iraq had "probably" continued producing chemical and biological agents after 1998. On 9 September it said "recent intelligence indicates" that "production of chemical and biological weapons is taking place". Uneasiness remained, however: to seasoned readers of JIC documents, the word "indicates" demonstrated the information was not of top quality, and the deadline for publication of the dossier was looming. A JIC staffer sent round an email on 11 September, saying: "This is ... a last (!) call for any items of intelligence that agencies think can and should be included."

At Vauxhall Cross, however, there was much excitement over a new informant who had come forward early in September. He was a senior military officer believed to be close to Saddam himself, The Independent on Sunday has been told, and he said he knew at first hand that Iraq was not only producing chemical and biological poisons, but also had stepped up output, building further facilities throughout the country. This was the information with which "C" - the traditional designation for the head of MI6 - had hastened round to Downing Street.

Sir Richard had mentioned the report two days earlier to the Prime Minister's foreign affairs adviser, Sir David Manning. Now he took Mr Blair through each of MI6's main sources on Iraq, including the "new source on trial". According to last week's report by the Butler inquiry into intelligence on Iraq, the MI6 chief "told us that he had underlined to the Prime Minister the potential importance of the new source and what SIS understood his access to be; but also said that the case was developmental and that the source remained unproven.

"Nevertheless, it may be that, in the context of the intense interest at that moment in the status of Iraq's prohibited weapons programmes, and in particular continuing work on the dossier, this concurrence of events caused more weight to be given to this unvalidated new source than would normally have been the case."

Translated from Lord Butler's mandarinese, the impact of this dramatic report was clear. Although it was not included in the dossier, launched on 24 September 2002, and was considered so sensitive that it was shown to only a handful of top figures, it was by far the most important of a tiny number of scraps of information which backed up the confident assertion in the dossier that "Iraq has continued to produce chemical and biological agents."

A week beforehand, Downing Street's chief of staff, Jonathan Powell, complained in an email about a previous draft of the dossier: "The document does nothing to demonstrate a threat, let alone an imminent threat, from Saddam ... We will need to make it clear in launching the document that we do not have evidence that he is an imminent threat." But in the foreword to the published dossier, written for Mr Blair by Alastair Campbell, Downing Street's former director of communications, and approved by the JIC chairman, John Scarlett, who claimed "ownership" of the dossier, the Prime Minister warns that the threat from Iraq is "current and serious".

"What I believe the assessed intelligence has established beyond doubt," Mr Blair goes on, "is that Saddam has continued to produce chemical and biological weapons ..." And the title of the dossier became "Iraq's Weapons of Mass Destruction", in contrast to "programme for WMD", as in previous drafts.

Virtually the only authority for any of these statements was the report from the "new source on trial". It was far more important than the 45-minute claim, which appeared four times in the dossier, and which became the casus belli between Downing Street and the BBC last year. The weapons scientist David Kelly committed suicide a year ago this weekend after being "outed" as the source for BBC reports that the 45-minute claim was unreliable, and should not have been included in the dossier.

Last week Lord Butler revealed that both the "45 minutes" information and the intelligence from the "new source" had been withdrawn last July, before the Hutton inquiry into Dr Kelly's death, setting off a row over whether Lord Hutton should have been told. Downing Street said the Prime Minister only found out from the Butler report. But the IoS has learned that MI6 discovered the untrustworthiness of its new source a lot earlier.

The week after the dossier was published, the Iraqi military officer was back in touch. If his first report had been just what the British authorities had wanted to hear, his second - the content of which is undisclosed - seemed "too good to be true", in the words of one source. What was more, he announced for the first time that his information was not first-hand. The realisation began to dawn that he was as unreliable as MI6's other main source; it is even possible that he was planting disinformation. Be that as it may, the Butler committee found that three of MI6's five main sources on Iraq's CBW had been discredited. The two still considered accurate were painting a far less alarming picture.

Mr Blair's defenders have insisted, as he did to Lord Hutton, that the dossier was never intended to make the case for war on Iraq - although Mr Campbell called it "one of the most important pieces of work developed during the entire build-up to the conflict" - and claim that four inquiries have now cleared the Prime Minister of lying about Saddam's WMD to take us to war. What the Butler report clearly shows, however, is that on at least one occasion he was told that the intelligence was tenuous, and that he could have asked searching questions of his spy chiefs if he had wanted to.

In October 2002, Congress gave President George Bush authority for war. The following month the UN Security Council demanded that Iraq give a full declaration of its WMD and let the weapons inspectors return. Yet when Iraq produced its declaration on 7 December, the JIC gave it only cursory attention, circulating an initial assessment which was never followed up.

If this did not indicate that the tide for war had become unstoppable, it could have been inferred from the fact that neither the Government nor the intelligence agencies thought it necessary to reappraise their views on Iraq's WMD after the UN inspectors repeatedly followed up MI6 and CIA leads and drew a blank.

Butler found this omission "surprising". Others might say it demonstrated a wilful refusal to seek the truth.

On Tuesday Mr Blair will open the Commons debate on the Butler report, hoping that once it is over and MPs join the rest of the country on holiday, the arguments over Iraq will cease. Government supporters have been seeking for some time to portray the Iraq issue as "boring", and, with power having nominally been handed over in Baghdad to an indigenous administration, they may succeed, barring some new and startling development.

This week could be the last chance for Mr Blair's critics to seek answers to their questions. Why did he not examine the intelligence more critically? Why has it taken him until now to admit that there might be the slightest flaw in the Government's WMD case? Does he feel he has anything to apologise for? And - a question no inquiry has ever been asked to examine - when did he promise President Bush that Britain would go to war at his side?

In the view of many, the elegantly written and unfailingly polite Butler report, while assigning "collective responsibility" and blaming no one, cemented the impression that Tony Blair decided on war first and sought the justification later. But nobody expects him to admit that, not even to himself.