n late 2004, in an atmosphere of frenzied speculation about war with Iran, Jack Straw - then Britain's Foreign Secretary - told the BBC that military action was "inconceivable."

"If I'd not done so, in my view we would have been involved in a firestorm inside the Labour government."

For the United States and Britain had recently invaded Iraq.

"It was impossible for any British government, but particularly a Labour government given what had happened in Iraq, to contemplate or have any dalliance with the idea of military action in Iran," he now recalls.

"I very consciously decided to close that issue down."

Today - with near civil war in Syria and the Middle East arguably more unstable than ever - military action is very much back on the agenda because of the belief in Washington and Jerusalem that Iran is closer to getting the bomb.

Now even Jack Straw thinks Western military action is possible - so much so, indeed, that he is issuing dire warnings against it.

"It could lead to a major realignment in international relations of a kind that we have not seen up to now," he says.

"You'd get huge divisions in the international community between the US and maybe the United Kingdom, on the one hand; other European countries somewhere in the middle; Russia and China, Brazil, India on the other."
Will Israel strike first?

So how likely is war?

In a striking series of interviews for BBC Radio 4's Analysis programme, we found that leading voices in Iranian, Israeli and American foreign affairs seem to agree on one sobering point - that a war with Iran over its nuclear programme is more likely today than it has ever been.

"The probability is that Israel will strike during 2012," says Ronen Bergman, an Israeli journalist who has recently completed a long series of interviews with senior Israeli leaders.

"The military in Israel is preparing for a strike, there is a huge military build-up," he says.

The crisis is coming to a head now because Israel's intelligence agencies are worried that Iran's nuclear facilities - especially at Fordow, near Qom where they have been enriching uranium - will enter a "zone of immunity" in nine months' time.

After that, they believe, Iran's nuclear sites will be buried so deep underground and dispersed so widely that they will be immune to an Israeli attack.

Iran points out that its uranium enrichment is allowed for civil purposes under the terms of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) which it has signed.

But because Iran has repeatedly violated the safeguards required by the International Atomic Energy Agency, the UN Security Council has ruled that it should accept additional obligations.

Israel's leaders cannot countenance even the risk that a regime like that led by Mahmoud Ahmedinajad will go nuclear, says Bergman.

"Once you face or you think you face a danger of another Holocaust, a threat of annihilation, then you need to do everything that you can in order to prevent this threat," he says.

For its part, the United States shares Israel's mistrust of Iran's nuclear programme. Despite condemning "loose talk of war", President Obama has emphasised the US could also act militarily if Iran does not negotiate in good faith.
A role for Hezbollah?

Some of President Obama's advisers go further.

"Israel has more limited capabilities, would do less damage to Iran's nuclear programme," points out Matthew Kroenig, who worked as a special adviser on Iran in the Pentagon until last year.

"So I argue that if military action is going to be taken, it should be the United States and not Israel."

Mr Kroenig thinks Iran's military response to a strike could be "managed" in a way that avoided escalation.

"Iran is most likely going to aim for some kind of calibrated response - to retaliate in some way but not to go too far," says Kroenig "because Iran knows that if they strike back too hard, they could lose their heads."

Despite agreeing to negotiations for now, Iran, too, seems to be preparing for conflict.

"If the US or Israel start, they would retaliate; they would not sit at home," says ambassador Syed Hossein Mousavian, a former lead Iranian nuclear negotiator, now based in America.

One obvious way Iran might retaliate is through its ally Hezbollah - the Lebanese militia movement has thousands of rockets targeted at Israel.

But ambassador Mousavian argues Iran's response would go far beyond that. Iran would be "confronting Israel directly and punishing all those countries which advocated war against Iran," he says.

"I cannot imagine US infrastructure, diplomats or personnel would be safe anywhere in the world. And you can imagine how a military strike would encourage all Muslims in the region to participate in a retaliation."
'Nuclear hedge'

Jack Straw, who did once manage to persuade Iran to suspend enrichment - in 2003, during his time as foreign secretary - thinks there is another way:

"In terms of how we handle this, it may be better to work on a policy of containment and isolation than it is to go in for a straight military attack," he says. "There are non-military means of putting pressure on a regime."

But why would Iran negotiate with the West if its true intention is to develop weapons?

"I think Iran would agree to some tactical limitations on their programme," says Mark Fitzpatrick of the International Institute for Security Studies, but "they would not give up the capabilities that they have to have a nuclear hedge."

By a 'nuclear hedge' he means a position where Iran has enough enriched uranium to make a bomb without actually doing so - and accepting that would mean compromise on both sides. Jack Straw argues that compromise and diplomacy will at least buy time.

"If the economic and social pressure on Iran is kept up meanwhile, then it will be in Iranians' interests, without any military action against them, to come in from the cold," he says.

"I have a sufficient faith in the idea of freedom and democracy to think that you will in time see a very different kind of government in Iran."

For the moment at least, diplomacy remains the preferred avenue in both Washington and London. But the rhetoric becomes tougher all the time.

"Nothing is off the table," said Britain's Prime Minister David Cameron last week at his meeting with President Barack Obama.

And what many western diplomats might call compromise is likely to be regarded as muddling through in Jerusalem.

The journalist Ronen Bergman recalls a conversation with the Israeli Defence Minister Ehud Barak: "All options are on the table," Barak said "but there's one option that is not on the table. This is the 'c' option: containment."

"It is our responsibility to defend the Jewish state and to take care of the future, the fate of the Jewish people," Ehud Barak continued, "and we take this very, very seriously."