With the air of a head teacher, he delivered his most crucial report of all

With his trousers a little too high around his ankles and his jacket awkwardly rumpled across his shoulders, Hans Blix rose from his seat at the edge of the Security Council. Mr Blix – who had just been invited to join the 15 members at their horseshoe-shaped table – looked grave, the usual easy smile notably absent.

Unusually, this was an open session of the Council. This meant a considerable audience for the United Nations' chief weapons inspector, who was presenting his report of the first 60 days of the resumed UN inspections in Iraq. Up to 300 pairs of eyes were on him in the chamber, with diplomats and members of the press cramming its public gallery. Around the world, watching on television, were millions more.

Mr Blix, who turns 76 in June, is not a man to flap. His tone, as always, was that of a headmaster. He scolds where he thinks scolding is warranted. He gives credit where credit is deserved. Referring to the weapons inspections, he said: "We seek to be both effective and correct." Mr Blix is nothing if not correct.

He has the calm that only a man of his years can project. He has been involved one way or another in protecting the world from cataclysm for the past 40 years, 16 of which saw him as head of the International Atomic Energy Agency (IAEA). He also has the calm of a man who is at the end of a career. This is his last mission. He can afford to describe things as he sees them. He has to curry favour with no one.

Yet few diplomats in the recent history have operated under such sustained and intense pressure. Mr Blix does not have to decide whether the world should go to war with Iraq. That is the task – as he likes to reiterate often – of the Security Council, or President George Bush and Tony Blair. But make no mistake: a single phrase from him, a single emphasis or adjective, could propel us into hostilities.

This is not what Mr Blix imagined for himself at this time of his life. He was on a cruise ship in the Antarctic with his wife, Eva, in January 2000, when he received the call from Kofi Annan, the UN secretary general, asking him to head a newly created body responsible for rooting out prohibited weapons in Iraq.

His thoughts until that moment were on retirement – summers spent on the small island he owns off the coast of Sweden and quiet hours writing a memoir and contemplating his already spent career.

Now Mr Blix finds himself with a singular burden on his shoulders. His inspectors are the final bulwark between peace and war in the Persian Gulf. And he, with each word delivered to the Council, can determine on which side of history we fall. His assessments may just be enough to restrain the bellicose impulses of Washington. Or they may be what tips us into war.

Not for 12 years, when the previous Gulf War broke out and the UN passed the ceasefire resolution that set the inspection process in train in the first place, have the corridors around the Council been so crammed with reporters, diplomats and observers. Or with so much nervous anticipation. Two priests, in dog collars and black suits, joined the scrum. Were they there to give us all, to give Mr Blix, a blessing?

Probably not. But so solemn was the atmospherethat help from God might have been appropriate. Ten minutes after the session was to begin, the chamber was all hubbub and milling of diplomats. Mr Blix came in the side door, only to be intercepted at once by Sir Jeremy Greenstock, the British ambassador, who, arms moving violently, imparted something to the Swede, but the rest knew not what. Go soft on Iraq? Don't give America cause to pull the trigger? Or just good luck?

Then, at last, came the call to order from Jean-Marc de La Sablière, France's ambassador and the Council's president, and at once the chamber was silent. M. de La Sablière went through the first few procedural niceties, giving the unseasoned among us time to twiddle through the dial on our ear sets to pass by Chinese and Italian and findthe clipped English translation.

Then came the invitation to Mr Blix to come to the table. Much of what he was about to say had been trailed through the pages of the world's papers for days. Nobody in the room expected any surprises from him or from Mohamed al-Baradei, the head of the IAEA, who would follow with his own report on the nuclear inspections on Iraq.

But what would be the mood of the headmaster? What marks would he give Bagdhad? If it was a B–, would that give Washington justification to declare the inspections a failure? Would a B+ buy his teams more time?

We knew fairly quickly that the student was not going to be treated lightly. The headteacher began by pointing to an earlier student who had done rather better. "Unlike South Africa, which decided on its own to eliminate its nuclear weapons and welcomed inspections as a means of creating confidence in its disarmament, Iraq appears not to have come to a genuine acceptance – not even today – of the disarmament, which was demanded of it," Mr Blix said.

There was brief praise. When it came to allowing inspectors access, Iraq was given good marks. It had "co-operated rather well ... the environment has been workable," Mr Blix conceded. Thereafter, however, he began to list all that was worrying him. It amounted, in the words of Sir Jeremy a little later, to "a catalogue of unresolved questions". As we, in the public gallery, heardthe admonitions and expressions of disappointment accumulate, we realised that Iraq's grade was beginning to slip.

There is, everyone agrees, a remarkable degree of trust among Council members of Mr Blix's judgement, even from most in the Bush administration, save the most hawkish. No one doubts Mr Blix understands his responsibility. He knows he cannot afford to misrepresent what he has found in Iraq. If he were to do that – even if his own pacifism impelled him to so – he could destroy the credibility not just of the inspections but of the UN as a whole for years to come.

So we listened with respect. And with deepening gloom. Mr Blix pointed to the recent discovery by inspectors of 12 empty chemical warheads and cast doubt on Iraq's claim that they had not been declared previously because of a mere oversight. Instead, he suggested, they could turn out to be the "tip of the iceberg" of undiscovered armaments.

He scorned Iraq's claims that it had no further documentation to prove its assertions that it had destroyed other unaccounted materials, including deadly nerve agents.

What Mr Blix did not do was tell the Council what it should do next. But he did, at the very end, make one thing clear: that he is still building his inspections effort in Iraq and, apparently, therefore, that he hopes he will be given more time to carry the process through. He gave a clear message to Washington: don't give up on us yet, don't attack Iraq yet.

Nor, finally, did the teacher – kind but stern at the same time – tell us what grade he planned to give the student. Anyone who was in the chamber yesterday could guess, however, at what it might be. It could just be a B–. Although Iraq might be lucky to get even that.