By Paul Reynolds BBC News Online world affairs correspondent in Washington

In the end, it came down to the difference between "shall" and "may" and to the importance of the word "consider".

At one time it was even proposed as a wedding present for the daughter of US Secretary of State Colin Powell.

Jack Straw: Key role in shuttle diplomacy

The story of the new Security Council resolution on Iraq - which will help determine whether there is to be war or peace - began on 12 September.

That was when President Bush went to the United Nations to announce that he would work through the UN to try to get Iraq to comply with previous disarmament resolutions.

That evening, at a reception in New York, the president thanked the UK Foreign Secretary, Jack Straw, for being the first to applaud at the key section of his speech in which he proposed a new resolution.

It was the opening of a close US-UK alliance on the resolution, which has been maintained.

The British always like to stay onside with the Americans; the Americans like to have at least one major foreign ally.

Robust language

The first task for the Americans and British was to draw up a draft text. The aim was to get a document robust enough to show that the Security Council meant business, but realistic enough to avoid a roadblock by France and Russia, both of which have vetoes on the council.

UN inspectors left Iraq in December 1998

It also had to avoid being too woolly, because that would upset the hawks in Washington. And the whole idea was to bypass the hawks.

The first effort was agreed on 25 September, after Mr Powell and Mr Straw had spoken three times on the phone the previous day.

It was certainly robust - too much so. It contained aggressive language about member states themselves getting involved in inspections, deciding for themselves if and when Iraq had not complied and giving themselves authority to launch an attack.

But it was not realistic. France in particular took the lead in opposing what it called "automaticity" - by which it meant that it was determined to break any automatic right of attack if Iraq failed to co-operate. It wanted a two-stage process, with a second resolution to authorise any military action.

Equally, Washington was determined not to be hobbled by any second resolution.

Alliance under strain

There was deadlock. France and the United States, who started as allies in the American war of independence, were continuing their more traditional role of rivals.

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The French President, Jacques Chirac, had no intention of being bounced into a decision. George W Bush did not want to be handcuffed.

The log-jam was broken on 7 October, after Mr Straw went to Paris to speak to the French Foreign Minister, Dominique de Villepin. He told the French that Paris and Washington had to "understand each other".

The breakthrough came the following week when the Americans made a key concession. They offered a second meeting of the Security Council to "consider" the situation if Iraq was in breach of the new inspections regime.

But the Americans did not commit themselves beyond that - they would not accept that military action would have to wait for a second resolution. A second meeting was as far as they would go.

But for the French, and by now for the Russians who had joined the French barricades, it was significant. It essentially broke the "automaticity" link. There would be no blank cheque.

Concessions

By the end of October, Messrs Powell, Straw and de Villepin became in effect junior diplomats, negotiating the new language line-by-line.

Searching Iraq

Deadlines for Iraq and the weapons inspectors under the resolution: 7 days: Iraq must confirm whether it will "comply fully" with the resolution 30 days: Iraq must reveal all programmes, plants and materials which could be used for weapons production 45 days: Inspectors must be allowed to resume their checks 105 days: Inspectors have 60 days from their arrival to report back to the Security Council but may report violations earlier

The British and Americans began to drop some of their harsher terms - which had probably been put in as negotiating fodder in any case.

There was a sticking point over one word. In the final version, Paragraph Four states that Iraq "shall be" in material breach if it makes a false statement about what weapons programmes it has. The French wanted "may" instead. They backed down. The negotiations moved on.

On 1 October, Mr Straw was in his constituency and rang the Russian Foreign Minister, Igor Ivanov. Mr Straw mentioned that Mr Powell had remarked that it would be nice if the resolution could be finalised before the wedding of his daughter the following day - it would make a nice present for her, since it offered a peaceful way out of the crisis.

Mr Ivanov, however, was not able to go that far, even for a wedding. Nor could the French. China was in the Franco-Russian slipstream.

New formula

There was still a way to go, but the way had been marked out. It still needed creative wording in the final few days.

The British UN Ambassador Sir Jeremy Greenstock came up with the text of an important paragraph (2) which gives Iraq a "final opportunity" to comply.

The essential positions of each side had been safeguarded. Both sides got a tough new inspections regime - including the removal of the special status accorded to the so-called presidential sites.

But the Americans and British had not agreed to come back to the council for authority to attack, and the French and Russians had not accepted that a new resolution in itself gave authority for action.

Creative ambiguity did the trick.

The parties will interpret the resolution as they see fit. That is often the nature of diplomacy.