The Big Question: What is at stake in the Geneva talks for Iran – and the West?

Why are we asking this now?

The most critical moment in the seven years of the international stand-off over Iran's nuclear programme is set for today, when diplomats from six world powers will face the chief Iranian nuclear negotiator in Geneva. The US, which has shunned any direct talks with Iran for 30 years, will take a leading role. The meeting, the first of its kind in a year, comes just days after the US, France and Britain dramatically revealed the existence a secret Iranian nuclear enrichment facility which they suspect to be part of Iran's efforts to acquire a nuclear bomb. The six powers (the five permanent members of the UN Security Council plus Germany) will demand "immediate and unfettered" access to the underground plant. They then want a commitment from Iran that it will enter into negotiations about stopping all expansion of enrichment activities that could lead to a weapons arsenal. As if tensions were not already high enough Iran has just engaged in two days of war games, test-firing missiles capable of reaching Israel or US bases in the Middle East.

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After the debacle over Iraq's WMD, how can we trust Western intelligence on Iran?

Hans Blix, the former chief UN weapons inspector and the man who led the hunt for what turned out to be non-existent WMD in Iraq, says the present crisis has echoes of the build- up to the war on Saddam, but with one big difference. Iraq had nothing. Iran has a lot of nuclear activity, and the capability to enrich uranium to weapons grade. Intelligence reports and inspections strongly indicate that Iran has, at various times, tried to acquire the means to build a bomb, although US and British intelligence agencies differ on the detail. The Americans, in a national intelligence estimate published in December 2007, concluded that work on "weaponisation" (converting nuclear material into warheads) was halted in autumn 2003. The British, Israelis and Germans suspect Iran has been trying to manufacture weapons more recently.

Western intelligence did pick up on the newly revealed nuclear site at Qom several years ago and Tehran has not denied its existence, just the charge that it has any military function or that there was a cover-up.

How worried should we be by Iran's nuclear programme?

News of a second, previously undeclared uranium enrichment plant conjured up mental images of bearded mullahs hunched over centrifuges in a bunker under a mountain near the ancient holy city of Qom. Put that with the knowledge that some devout Iranian Shias, including President Mahmoud Ahmadinejad, are followers of Mahdi, the so-called "Twelfth Imam" who they believe, will return only "in a time of chaos" and you could reach some apocalyptic conclusions. An alternative view is that the mullahs are entirely rational politicians motivated by the desire to cling on to the power they seized in the Islamic revolution 30 years ago. They certainly also feel encircled in the Middle East and may want to convey the impression they have a nuclear deterrent.

What we know for sure is that Iran is enriching uranium – which they claim they need to do to generate atomic energy. But the Qom plant is on a Revolutionary Guards base, and is far too small to be of any possible use in a civilian nuclear programme. To make weapons they need to enrich their uranium to a much higher level than required for a fuel reactor. With 3,000 centrifuges the scientists at Qom would need about a year to enrich raw uranium to bomb grade. But they already have access to plutonium and low enriched uranium and enriching that would take less time experts believe. They also have both short and long-range missiles although nobody believes they are yet at the stage of weaponisation, in other words combining a nuclear warhead with a missile. Another concern is that the UN nuclear watchdog, the IAEA, inspects only nuclear sites which Iran has reported to it, so it could be hiding a third, or even a fourth undeclared plant.

What's the US strategy and does the world agree?

Barack Obama's plan is to up the ante by threatening to tighten patchy existing sanctions to a regime of harsh UN sanctions if Iran fails to come clean and enter negotiations by December. If he could achieve a united front, it would be a big victory for his vision of multilateralism. But there are cracks which Iran will be quick to exploit. The US President has gone some way in persuading Russia to stop blocking sanctions in the UN Security Council. But Moscow sells energy technology to Iran and still sees its links with the regime as a means of gaining the upper hand in its dealings with the West. China buys huge amounts of oil from Iran; is eager to preserve that energy relationship and typically does not trust the notion of interventionism. China would veto any kind of embargo on refined oil shipments. Winning agreement on a toothless sanctions package would be as damaging as no sanctions at all, because they would not work.

Can the Iranian opposition help?

We saw the ugly side of the clerical regime after the June elections. Democracy protesters have been tortured and raped in prison, according to witness accounts. Scores have died, disappeared or been paraded in mass show trials. But the repression does not mean Iranians don't still criticise their President (challenging the Islamic system of government is a different matter). Many openly blame Mr Ahmadinejad's bellicose handling of the outside world for the country's economic isolation. Yet, most regard the nuclear programme, and the idea of having a capability equal to Israel's, as totemic, a symbol of national pride. Opposition leaders, including Mirhossein Mousavi, support the nuclear policy and worry about the impact harsh sanctions on poorer Iranians. Indirectly however, the courage of the grassroots movement is helping. Their protests flushed out the weakness of the regime and the fissures in its ranks. A nervous Ahmadinejad will not want a fight on two fronts so this may push him into eventually seeking an accommodation with the West.

Could the meeting yield a breakthrough?

It is hard to find anyone who doesn't expect failure, given the mistrust. Unlike the previous US administration, which would not talk until the Iranians first committed to suspending enrichment, Barack Obama is imposing no preconditions. But Iran reacts badly to threats of punishmentand its representative Saeed Jalili will not be authorised to make any decisions today that don't have to be referred back up to the Supreme Leader Ayatollah Khamenei.

Could this crisis end in war?

Mr Obama's foreign policy is underpinned by a desire to tackle problems like Iran through multilateral dialogue rather than go-it-alone military adventures. But in the current inflammatory atmosphere, Iran is being portrayed literally as a ticking time bomb. With growing pressure from Israel, Mr Obama could conceivably find himself hurtling towards a confrontation he doesn't want, in an effort not just to contain Iran, but to avoid looking weak.

Can Iran's nuclear ambitions be kept in check peacefully?

Yes...

* The mullahs face a groundswell of dissent and need to negotiate.

* Washington could offer to restore diplomatic ties conditional on a freeze in nuclear activity.

* Offer Iran a role in solving Afghanistan and other regional problems. This would take the poison out of the present impasse.

No...

* The clerical regime has shown its duplicity so many times it can't be believed or trusted to negotiate.

* The discovery of a second nuclear enrichment plant means Iran could be hiding a third or even a fourth.

* The Iranian opposition rely on the West to intervene forcefully now for the sake of human rights.