Charles Kennedy: Tony Blair is not in the dock, but the court of public opinion will judge him

Lord Hutton is particularly deadly when he hesitates before choosing exactly the right word

This morning, the Prime Minister will be a witness in court, though not literally in the dock. Ironically, though the Hutton inquiry is headed by a judge, it is not a judicial inquiry - even though it is taking place in the Courts of Justice. Lord Hutton has no power to require attendance or demand to see documents and papers and his remit is to focus on the tragic circumstances which preceded the suicide of Dr David Kelly. That, in my view, is a pity. The nation deserves the full, searching, light of judicial scrutiny to play on the whole of the controversial issues surrounding the lead-up to the Iraq war.

Yet Tony Blair's appearance will nevertheless be of extraordinary importance; and although he's not on trial, he will certainly be appearing before the court of public opinion, and may be harshly judged.

Lord Hutton has been careful not to exceed his initial remit - and appears to be interpreting it as an investigation of whether the Government abused its "duty of care" to Dr Kelly.

We have been drawn a picture of a civil servant who was apparently used to dealing with journalists in his own specialised area of expertise but who, otherwise, had spent his working life away from the public arena. We have heard that the Prime Minister was closely involved in the processes leading up to the naming of Dr Kelly, and that has prompted some clear lines of inquiry. Did he approve the MoD's "naming" strategy and did he also realise, that in the process, he was also approving the shaming of Dr Kelly? If so, why did he want Dr Kelly's name made public?

We have heard that he wanted Dr Kelly properly prepared before his evidence to the Foreign Affairs Select Committee. That begs the question whether Mr Blair wanted Dr Kelly to undermine the BBC journalist Andrew Gilligan's story that Downing Street had tried to sex up the intelligence information that was used as public evidence in the case for war.

Above all, was Dr Kelly pressed into giving evidence to try to add to or restore the Government's reputation? Which poses the ultimate question of whether the Prime Minister's judgement was so skewed by the need to restore trust in his government that it overrode the need to consider the human consequences for Dr Kelly.

These are the immediate questions at the heart of Dr Kelly's tragedy. But if that is all that Lord Hutton seeks to achieve when the Prime Minister appears tomorrow, it will not be enough. It won't do, because the nation also needs to know conclusively whether or not we were taken to war on a false premise.

In that context, Lord Hutton's opportunity is unparalleled. As matters stand, it is highly unlikely the Prime Minister is going to agree to any further public investigation of these events once the Hutton report is published. Yet the glimpse - the tantalising peek behind the curtain of secrecy that normally obscures the operation of government - that the lines of questioning have already elicited, has provided a wealth of evidence to suggest that what we were told about the situation in Iraq, in the run up to military action earlier this year, was by no means the whole story.

One of the most astonishing revelations of the inquiry came from Jonathan Powell, the Prime Minister's chief of staff. In an e-mail, he said that on the basis of the intelligence contained in the September dossier, which was used to explain the threat from Saddam Hussein, the Government could not claim that Saddam was a threat even to his neighbours, let alone the West. Yet a week later the Prime Minister told the House of Commons that the threat from Saddam was "serious and current". How does the Prime Minister square those two comments?

Yesterday, the Defence Secretary, Geoff Hoon, told the inquiry that Dr Kelly - who has now been revealed as the Government's top expert on Iraq's weapons of mass destruction - believed that there was only a 30 per cent chance that Iraq was producing chemical or biological weapons again. If he, a former UN inspector with continuing contacts inside the regime, believed this, why did the Prime Minister feel comfortable claiming - as he did in the dossier - that Iraq's WMD programme was "real, active ... up and running"?

In light of Dr Kelly's doubts - which were apparently shared by others in the intelligence community - Downing Street nevertheless continues to assert its confidence in the immediacy of the WMD threat from Iraq. So can the Prime Minister explain why the Hutton inquiry has brought to light so many e-mails apparently trying to change phrases like "sought uranium" to "secured uranium" and "may be capable" to "is capable", and endlessly hunting for more substantial material?

The obvious answer - clear to anyone who has taken much interest in the detailed coverage of the proceedings - is that the case for war was exaggerated.

This is hugely important because the fact is that when Parliament was being asked to vote in favour of military action, those of us who opposed the decision to go to war did so because we believed the case was too weak; in particular we were not convinced that Saddam had either the means, or the will, to be a serious threat. What we have heard has simply reinforced those doubts.

I do not believe that Lord Hutton would be straying beyond his remit if he challenged the Prime Minister about this in detail because the picture that has emerged of Dr Kelly is of a decent, serious man who was profoundly concerned about the build-up to war and well-qualified to advise the politicians about the real threat Saddam Hussein posed. We know he was immersed in his work, anxious that his advice should be respected, concerned about what might happen to his Iraqi contacts if there was conflict. There can be no error that is more desperate than a war undertaken on an inappropriate basis. Dr Kelly was in an excruciating position.

Every week, in the House of Commons, when Tony Blair appears at Prime Minister's Questions, he is, in a sense, on trial. As a party leader, I have a privileged place among the 650 or so potential inquisitors, because, together with the leader of the Conservative Party, I am guaranteed the right to ask a question. I can truly say I know it's not easy - getting to the inner Blair. The Prime Minister thrives in that environment. He is a barrister by training - and, perhaps, would prefer to be framing the questions rather than the answers; but after seven years in the job, he's quite brilliant at revealing only the information which best suits him.

But Lord Hutton and his able assistant, James Dingemans QC, have proved skilful in their quiet, yet courteous, probing of their witnesses and Lord Hutton, it has been observed, is particularly deadly when he hesitates before choosing exactly the right word. This will be an astonishing confrontation - of vital importance to our democracy.

The writer is leader of the Liberal Democratic Party