Wearing his mullah's robes and turban he smiled broadly at a sea of television cameras and the crowd of journalists flown in for the occasion before announcing that Iran had - voluntarily and without succumbing to any kind of pressure - agreed to the world's nuclear demands. The conference took place after several hours of talks between the four men.

Rohani insisted the country is not bowing to a strongly-worded resolution passed in September by the International Atomic Energy Agency (IAEA) to disclose all nuclear activities, sign a protocol allowing snap inspections and suspend uranium enrichment by 31 October. But he agreed to voluntarily go along with the demands to show goodwill.

'The protocol should not threaten our national security, national interests and national pride,' he said.

While the decision to sign was made of its own volition, Iran has come under considerable international pressure. Apart from the US, the EU, Russia and Japan have all demanded co-operation with the IAEA. A long-discussed trade agreement with the EU was directly threatened by the crisis, as was the signing of a major oil field development with Japan. Further ahead, IAEA dissatisfaction could conceivably have led to wider foreign sanctions.

A statement released after the meeting spelled out Iran's commitments. It will engage in full co-operation with the IAEA and give transparent answers to all outstanding questions and correct past failures. It will sign the additional protocol, which it will abide by until formal ratification has taken place. It will also suspend all uranium enrichment and processing activities as defined by the IAEA for an unspecified length of time.

In return, UK Foreign Minister Jack Straw, French Foreign Minister Dominique de Villepin and German Foreign Minister Joschka Fischer made principle-only commitments. They recognised Iran's right to a peaceful atomic power programme. They pledged that co-operation with the IAEA and signing the additional protocol in no way diminished Iran's sovereignty or national dignity. More concretely, they said Tehran would find it easier to get access to advanced nuclear technology and fuel once it had proved its nuclear innocence. Gaining Western nuclear technology has always been one of Iran's stated goals. It has insisted on its rights - endorsed by the non-proliferation treaty (NPT) - to assistance in developing a civilian nuclear programme. Under pressure from the US, European countries have for the past 15 years been reluctant to allow their technology to fall into Iranian hands. A German contract to help build the Bushehr power plant was derailed in the late 1980s at the behest of the US. In securing the hint of European technological help, Iran can present the deal as an equal exchange.

Reformist and moderate conservative newspapers in Iran interpreted the latest nuclear deal as a major diplomatic coup, citing the fact that three such important foreign ministers had made an unprecedented simultaneous trip to solve the problem. The English-language Iran News hailed the agreement as the 'clearest-cut diplomatic victory for Iran since [the] revolution'. And the moderate conservative Entekhab said the deal was a major defeat for the US.

The three ministers - particularly Straw - reiterated time and again after their meeting with Rohani that Iran's sovereignty was in no way being threatened. Tehran has often said it believes the additional protocol would be used by hostile powers as an excuse to conduct military espionage.

Some hardline conservative newspapers did denounce the deal as a sell-out, indicating a possible rift between conservative pragmatists and hardliners, who may want to be appeased with future concessions. Jumhuri-ye Islami, the most right wing of Iran's papers, railed against what it called a US-sponsored 'disgrace'. But fears that it would be impossible to strike a meaningful deal with a country where political division has become a watchword were convincingly allayed by the fact that Rohani acted as point man.

In the past, most of Iran's more encouraging statements were made by staunch reformists in parliament, the president's office or the Foreign Affairs Ministry. They have often been contradicted by more hawkish sentiments expressed by Supreme Leader Ali Khamanei or the jurists who sit on the Guardians' Council, the Council of Experts and Expediency Council - the hardline bodies that hold the real strings of power.

But this time, it became evident senior conservatives had chosen the path of pragmatism and wanted to do a deal. Rohani is secretary of the SNSC - Iran's top committee for questions of foreign and security policy. Although the SNSC is chaired by the reformist Khatami, the bulk of its members are from conservative institutions like the supreme leader's office, the judiciary and the armed and security forces.

Rohani himself is a pillar of the conservative establishment. A member of the Tehran Militant Clergy Association, he had a parliamentary seat from 1980, chaired the foreign affairs committee and organised much of the political ideology department of the armed forces. In 1988, he stood in for Ali Akbar Hashemi Rafsanjani, then acting commander-in-chief of the armed forces. He has the ear of all important parts of the right wing and an official position that gives him seniority over most of the left. By negotiating on behalf of Iran, he was making a deal that comes straight from the top.

On the European side, the agreement was months in the making. A letter, drafted by France but also signed by the UK and Germany, was sent to Iran in August. It made the initial proposal of full compliance in exchange for technology. At first, it appeared to have been rejected.

But that was before the IAEA's damning September report. Although the US demand for a straight condemnation of Iran won no support, the IAEA decided to give Iran the 31 October ultimatum. Backed up by the real prospect of sanctions, the Iranian leadership realised a crossroads had been reached: either follow the route of North Korea as an international pariah with an admitted weapons programme; or accept the IAEA demands.

The European carrot had effectively been backed up by a convincing US stick. But closer analysis shows the end result was a victory for everybody. Europe did not want to enforce sanctions on Iran that could damage valuable economic ties and undo years of politically-expensive diplomacy.

'It is an important day for Europe because we are dealing here with a major issue. We are talking about proliferation, which as everyone knows, is a huge challenge to the world community,' said De Villepin at the press conference.

Even the US, despite the aggressive position of its own hardline neoconservatives, has no appetite now for another international crisis. It wanted a reason to restrain its own - and Israel's - more aggressive instincts. But at the same time, it can at least claim independence from the latest agreement if it wants to send a tougher message to Tehran in the future.

And it does have some reason for suspicion. Over the past year, a series of revelations about Iran's nuclear programme have dismayed the IAEA. A uranium enrichment site at Natanz was only admitted to after its location was revealed by the opposition Mujahedin-e Khalq Organisation. Later, weapons-grade uranium traces were discovered by IAEA inspectors at the plant. The UN nuclear watchdog is now demanding Iran promptly give it satisfactory answers about those traces and about other aspects of its nuclear programme.

'[IAEA chief Mohammed] ElBaradei hopes and expects that in the next few days Iran will deliver. a full declaration of all its past nuclear activities and an official notification of its readiness to conclude an additional protocol,' said IAEA spokesman Mark Gwozdecky after the agreement was signed.

This is where the pitfalls lie. Agreeing to co-operate is very different from actually doing so - as the world discovered with Saddam Hussein. Sceptics contend that Iran is merely buying time so it can thwart the inspections regime at a later date. Will Iran allow inspectors access to all facilities they request? Could Iran recommence uranium enrichment and under what circumstances? Will the IAEA be satisfied with the answers it gets to outstanding questions?

'The proof of the value of today will depend not just on the words in the communique... but above all on the implementation of what has been agreed,' said Straw at the press conference.

Iran did hand over a document clarifying its nuclear position the day following the meetings, but the road ahead is not clear. And from the statements made by Straw, De Villepin and Fischer, Iran does not have free rein to delay. No time limits have been spelled out, but Europe, as well as the US, needs to see prompt co-operation by Tehran.

The task will not be easy as it is counter-intuitive in a country so often abused by imperial powers. But the good news is that a serious decision has been made to at least pursue the path of peaceful co-operation. n