It has become an annual event in international affairs: the "Iran crisis". Belligerent politicians and febrile commentators refer to the "drumbeat of war", the "ticking clock" and how "all options are on the table". My own, oft-repeated favourite is "the window of opportunity" - to thwart Iran's nuclear programme through military means - "is closing". Is it? Is it really? For more than a decade now, the alarmists have warned that Iran is - take your pick - "one year", "two years" or "four to five years" away from acquiring nuclear weapons. Wrong, wrong, wrong. These random deadlines have come and gone without Iran building the bomb. The window is jammed wide open.

As the leading US arms control expert, Jeffrey Lewis, of the Monterey Institute of International Studies, asked on his blog on 7 November, in the wake of the latest bout of feverish commentary on Iran's nuclear programme: "Just what technical or political fact has brought the deadline to the crossroads?"

“The driver in all of this is Israel," a former senior MI6 official tells me. As long ago as November 2002, the then Israeli prime minister, Ariel Sharon, demanded that the Bush administration turn its full attention to Iran "the day after" the Iraq invasion was over. The Israelis now have the backing of (Sunni) Arab states, alarmed by the prospect of (Shia) Iranian nukes. According to a WikiLeaks cable, Saudi Arabia's King Abdullah urged the US to "cut off the head of the [Iranian] snake".

Iranian uranium

However, consider three very important issues. First, there is no hard evidence that Iran is in possession of nuclear weapons or working on a nuclear weapons programme. The Iranian government insists that its enrichment of uranium is for domestic energy only. And you might not have guessed it from the coverage on CNN or Fox News but, in 2007, the US intelligence community estimated with "high confidence" that Iran had halted its alleged nuclear weapons programme in 2003 - a view reiterated in testimony to Congress by the US director of national intelligence, James Clapper, in March.

Even the International Atomic Energy Agency's (IAEA) report of 8 November on Iran, which prompted the latest bout of sabre-rattling, failed to produce a "smoking gun". There were some ominous references to weapons-related research and development, high explosives, computer simulations and assistance from foreign scientists - much of this based on "secret intelligence" from western governments. But the IAEA's report provided no new information on whether Iran is building - or intends to build - a nuclear weapon.

The UN nuclear watchdog's credibility is at stake here. Under its former director general Mohamed ElBaradei - who once described the Iranian nuclear threat as "hyped" - the IAEA stood up to US pressure in the run-up to the 2003 Iraq invasion. Yet, according to State Department cables released by WikiLeaks, ElBaradei's replacement, the Japanese diplomat Yukiya Amano, told the US government in 2009 that "he was solidly in the US court on every key strategic decision, from high-level personnel appointments to the handling of Iran's alleged nuclear weapons programme".

For the sake of argument, however, let's assume Iran is indeed bent on acquiring nuclear weapons. The second key issue to consider is whether or not such intent would merit a military response. In a world where nine nations - the US, the UK, France, China, Russia, India, Pakistan, Israel and North Korea - are believed to possess nuclear weapons, would a tenth make a such a difference (beyond a slight shift in the balance of power in the Middle East)?

No threat

I'd prefer to see a global ban on nuclear weapons but, in the absence of such a utopian measure, are we expected to believe that Iran would behave any more irrationally or irresponsibly with its (hypothetical) nukes than North Korea? Or Pakistan? Paul Pillar, the CIA's national intelligence officer for the Middle East between 2000 and 2005, wrote last month that, contrary to conventional wisdom, there is nothing "in the record of behaviour by the Islamic Republic that suggests irrationality".

In spite of the claims from the Israeli prime minister, Benajmin Netanyahu, and his neocon allies in Washington DC, the truth is that a nuclear-armed Iran wouldn't be an "existential" threat to the (nuclear-armed) state of Israel. According to the former Mossad chief Ephraim Halevy, in a speech on 3 November: Iran's nuclear capabilities are still "far from posing an existential threat to Israel".

And the Israeli defence minister, Ehud Barak, who visited the UK earlier this month to build support for a military attack on Iran, has admitted that the ayatollahs in Tehran are unlikely to order the dropping of a nuclear bomb on the Jewish state. "Not on us and not on any other neighbour," Barak told Haaretz in May.

Above all else, however, an attack on Iran's nuclear facilities would be self-defeating. It would prompt an enraged Iranian government, backed by a united Iranian public, to speed up the country's nuclear programme and drive it deeper underground - and outside the IAEA's purview. As Robert Gates, the then US defence secretary, conceded in May 2009: "A military attack will only buy us time and send the [nuclear] programme deeper and more covert."

Hans Blix, the UN's former chief weapons inspector, agrees. "You cannot scare a country away from going down the path of [building] nuclear weapons," he tells me. Diplomacy is the only viable option. In a warning that should set off alarm bells inside foreign and defence ministries across the west, he adds: "If the Iranians haven't yet made up their minds to make a nuclear weapon, then they will certainly do so once they have been attacked."