The guns are waiting for Sir Richard

Scott's arms-to-Iraq inquiry has got Whitehall running scared. Now begins the real fight for credibility

These are critical days for the Scott Inquiry into the arms-to- Iraq affair, which has the potential to cause the biggest detonation in Whitehall for a generation. The inquiry is running late, is already being privately attacked as unfair by politicians and may face legal challenges by civil servants it criticises.

Tonight Sir Richard Scott is to speak out in a lecture about his views on ''Fairness in public inquiries''. This is unprecedented for the chairman of an uncompleted public inquiry. Why is he doing this? The answer from the inquiry is that it was a long-standing engagement - matter of honour to fulfil it, judge had anyway expected to have finished by now.

But given the mounting level of private attacks on the fairness of his own inquiry, and the rising whispering-campaign in Whitehall, for Sir Richard to go public now is, at the very least, convenient timing. There is a battle for authority going on between the judge and those awaiting judgement.

Its result will be of great political, even constitutional, importance. Will the judge be regarded by the ultimate court, public opinion at large, as Mr Valiant-for-Truth, or (as some ministers hope) a nave and arrogant incompetent? If it's the former, ministers will resign, Whitehall will be shamed and the authority of the Major administration may be finally spent.

If Scott is partly discredited by the time he publishes, however, then most and maybe all of those criticised will be able to fight back, the damage can be limited, Sir Humphrey will breathe a sigh of relief and the Government will be able to move swiftly on.

So questions that may seem technical or legalistic, to do with the inquiry's remit and procedure, have, in reality, an intensely political flavour. Sir Richard Scott is no longer involved merely as an arbiter; he has been unwillingly drawn into a contest in which he must defend his own status and conduct.

What, then, are the main lines of attack on his status? There is, first, the complaint that his procedure flouts natural justice because witnesses were not allowed to be represented by their own lawyers, or have their lawyers cross-examine other witnesses.

Lord Howe, who criticised Scott last year for sitting as prosecutor, judge and jury, is leading the attack on "natural justice'' grounds, and speaking for civil servants, particularly in the Foreign Office, with whom he has been in contact. Howe has told the judge that he believes he has failed to follow established precedent for such inquiries. He wants Scott to allow at least further closing submissions from departments and agencies, and feels that it is wrong that the judge alone has seen the whole picture.

But Howe is unlikely to get much change from Scott, who believes the former Foreign Secretary's complaints are based upon his career in the adversarial English judicial system; whereas this inquiry, based first on reams of documents, and then on written and verbal evidence, is an inquisitorial event, designed to determine a complex truth. His lecture tonight will include a detailed but sharp-edged defence of the system he's following.

Lord Howe is in crusading, not defensive, mode. He sees himself as speaking up for those who cannot speak for themselves. Waiting behind him is a silent army of politicians and officials that has closely followed his every move and bided its time.

His criticisms could, in theory, open the door to judicial review on behalf of civil servants who have been criticised. Supporters of the inquiry are worried that, after setting the inquiry up, covert government backing might eventually be given to a campaign against its authority and findings - which really would provoke a constitutional crisis.

The other line of attack comes from friends of the inquiry who are concerned that Scott has simply been too ambitious. "I suspect it's almost navety, but he's marching straight towards the guns ... he's taking on the whole of Whitehall," says one.

And it is certainly the case that Scott has interpreted his remit, which was broadened after opposition protest, pretty widely. It is well known that five ministers have been looked at particularly carefully, of whom one, Kenneth Clarke, has promised to offer his resignation if he is criticised. The word is that he may come to see this as a rash offer.

But Scott, it seems, is gunning not only for individuals, but also for the Whitehall culture which hoards information in departments, and within departments, and is obsessively reluctant to communicate, either to itself or to Parliament.

Sitting writing his report in solitary splendour, the judge is believed to be criticising not just a series of ministers and ex-ministers, but the closed central core of the system of British government - the key departments, senior officials, MI6, the government lawyers, the law officers. Thus an exercise originally intended to buy the Government a few weeks' breathing space has turned into a constitutional review.

Sir Richard's admirers see this as both entirely logical, given what the inquiry has revealed, and as characteristically brave. His political detractors portray him as an isolated figure with a gleam in one eye and the other eye fixed self-importantly on posterity.

Whitehall certainly believes in the ambitious nature of the looming report. As the weeks and months pass, the tension and rising alarm of Britain plc has become palpable. Departments have been responding in the only way they know how: with massive salvoes of paper. As Scott sends out draft sections of the report to those who are criticised, he gets back mounds of new evidence. And because of the Howe-type criticisms, he is under pressure to sift them with meticulous care.

The result is that the inquiry is way behind schedule. The judge and his people, who have complete control over the publication date, are still hoping to publish it by the beginning of July. But this depends on the reaction to the next set of drafts, which are the hyper-sensitive ones relating to the collapse of the Matrix-Churchill trial itself. Given how much paper has already been fired back at the inquiry team, suspicion that the report may be delayed until November - a full year late - is hardening.

Sir Richard has huge power simply because, if it comes to a battle for credibility between himself and a group of politicians then, given the nation's mood, the politicians are so likely to come second. But this is a critical period, during which some observers believe the whole inquiry could veer out of control, overburdened by its own ambition and the fear and paperwork it has generated in Whitehall.

The inquiry team itself radiates quiet confidence. But it is certainly possible for Sir Richard to overplay his hand. Any hint that, in the end, he has been less than scrupulously fair will be seized upon by a system which now feels threatened and which, in its heart of hearts, denies his right to stand in judgement over it.

He may be a good judge and a fair man - qualities he will seek to demonstrate tonight. But Sir Richard had better understand that Whitehall is getting ready to rumble. He's going to have to prove himself a fighter, too.