It is difficult not to see the looming crisis on Iran through any other optics other than our experience in Iraq. So much of the commentary on the left is falling into this trap. "We got it wrong on WMD in Iraq so we can't and shouldn't believe what we are told on Iran."

Yes, we should all be more exacting in the questions we ask after the painful lessons from the flawed intelligence on Iraq. But if this means we fail to take the threat of Iran seriously we will be making a terrible mistake. The memories of Iraq are fuelling some basic misconceptions over Iran that need to be cleared up. We are not and should not 'sleep walk' into a war, but if we take the military option off the table, we may paradoxically bring a conflict closer.

Is the threat exaggerated, just like in Iraq?

This is not like Iraq, where our assessment of the threat was based on hazy intelligence. Many of the unacceptable Iranian activities, such as uranium enrichment, are happening in the plain sight of IAEA inspectors, following their exposure by Iranian opposition groups and Western intelligence agencies in 2002. Intelligence evidence of many other aspects of the programme, such as weaponisation, were studies by the IAEA for years before the agency declared the evidence 'credible' in its November 2011 report.

I am not one of those who think Iran is irrational. On the contrary, their pursuit of nuclear weapons is a highly calculated strategy to maximise their power in the region. But the fact that they are rational does not make their programme benign.

Iran's already sponsors radicalism and terror not only throughout the Middle East but across the world from South America to Asia. They already position themselves as a pillar of resistance against Western influence in the Middle East, against the Middle East peace process and against any international attempts to resolve the crisis in Syria. They already call for Israel's destruction and provide the arms and money for extremist groups on Israel's borders to perpetuate the Israeli-Palestinian conflict. They already hope to bully and intimidate their Gulf Arab neighbours into accepting their regional leadership and turning away from their alliances with the West. The acquisition of nuclear weapons capability, in bald defiance of American and international, will only further enhance their capacity to advance this dangerous agenda.

William Hague has been clear on this issue since long before his time as Foreign Secretary. He sees the threat from the perspective of Iran's Gulf Arab neighbours. They are among the countries most immediately threatened by Iran. Hague understands also that British national interests are directly affected. Look at the percentage of inward investment into Britain from the Gulf. Just think what would happen to those trade interests if a nuclear armed Iran, for whom Britain is the 'little satan', became the dominant power in the region.

Our government also knows that the Iranian threat is real. There is no significant difference in assessment between Britain, the US and Israel. If anything, the UK shares Israel's concerns that the US has tended to understate how advanced Iran's programme is.

Are we sleepwalking into a war?

Today, the US and Europe have a well-coordinated policy of squeezing Iran through crippling sanctions. The decision for the West to give up that track and resort to military action will ultimately be an American one. Of the Western powers, only they have the military capacity to seriously degrade Iran's nuclear programme.

Obama understands the scale of the Iranian threat and sees it in a wider context. His vision of a nuclear weapons free world was the subject of his first international speech in Prague in 2009. In recent months he has been clear that the US will not allow a nuclear Iran.

We cannot underestimate his capacity to take decisive military action. In the last chapter of Bob Woodward's brilliant book on the Obama decision making process on the Afghan surge, Woodward asks Tom Donilon what he has learnt about his President. Donilon said that the president thinks if you are patient and resolute then others will come round to your thinking. This is an indication of his single mindedness.

He made the decision on the hit on Bin Laden when others would not take the risk and he allows the repetitive use of lethal force by US drones even in sovereign Pakistani territory. We know from recent statements from US officials that preparations have been ongoing under his administration for a credible military option against Iran.

But if Obama decides to take military action it will not be for lack of attention or through carelessness. It will be an act of clear rational assessment of costs and balances, in the knowledge that no choice, including the choice to do nothing, is cost free.

We also know that the US believes Israel does not have the capability to do a military operation well enough. Their assessment is that Israel could not reach all the relevant sites and could only set the programme back a few years. The US could do a much more comprehensive job. For that reason the US does not want Israel to launch a military strike. But at the same time they do not want to be pushed by Israel into a decision on military action in an election year.

Can Israel be persuaded to wait?

No one in Israel is gung ho for action. It will be Israeli citizens who will have to take cover in bomb shelters as Iran and its allies retaliate with thousands of rockets on Israeli towns and cities. But the noise coming from Israeli officials shows that they are losing patience. Israel's sense of urgency comes from a fully understandable feeling of dread at what the region will look like for them with a nuclear armed Iran.

What's making Israel particularly jittery right now is that key aspects of Iran's programme are moving towards what Israeli Defence Minister Ehud Barak calls a 'zone of immunity', meaning the point at which Israeli weaponry will no longer be able to damage them. Iran is already starting to operate an underground uranium enrichment facility in Fordow which may be impossible for Israel to bomb.

After that point, the better equipped US forces may still have a viable military option, but Israel does not like to leave key questions about its security in the hands of others, even its closest allies. Israel knows if it were to go it alone the risks would be enormous and the impact on the programme less than if the US were to act. But Israel has a deeply ingrained political culture of self-reliance.

It is a lesson Israelis take from Jewish history. They should never rely on others to defend them. Even if an Israeli strike only sets the Iranian programme back a few years, they may reason that this could buy time for other developments which undermine the Iranian regime.

That we have reached a point at which Israel may feel the need to act alone, without warning, indicates that we have not acted decisively enough before now. The severity of the sanctions is now catching up with the severity of the problem, but it is late in the day. Asking Israel to wait through 2012 and see if the sanctions will work means asking them to potentially give up their capacity for independent action.

It is not clear if Israel would warn the US in advance if it were to launch a military strike. It could inform the US what it is about to do in the hope that the US will step in. But this risks the US telling Israel flatly not to do it. Israel might be willing to act without an explicit US 'green light', but it is much harder to act in the face of an explicit demand from the US to stop.

Should we be taking the military option off the table?

The conclusion this leads to is that if we want to remain in control of the situation, we need to be absolutely clear in our determination that we will not allow Iran the capability for nuclear weapons. We need to be equally clear that we will consider all means, including military means.

If Israeli leaders suspect that the rest of the world is going to duck its responsibility, it is more likely to conclude that it has to act alone, despite the consequences. Equally concerning, is that if our Gulf allies think we are going to abandon them whilst Iran get nuclear weapons they are going to start considering whether they need to appease the playground bully. And if Iran hears that military action is not an option, they are going to be encouraged to hold out against the sanctions, in the belief that once they reach nuclear armed status, they will be able to negotiate with the world from a position of strength.

Iran, therefore, is not Iraq. To maintain the best chance of preventing a conflict, we need to keep all our options very much available.