As the mullahs press ahead with the construction of a new heavy water reactor at Arak and resume the production of centrifuges, the prospect of an Iranian nuclear bomb looms increasingly large. Why, though, would such a development be a cause of serious concern for the watching world?

It is not because, as often claimed, a nuclear Iran would be able to pursue a much more aggressive foreign policy against its archenemy, Israel, and destabilise the entire Middle East. Reuel Marc Gerecht of the American Enterprise Institute, for example, has argued that the Iranians would feel at liberty to use the bomb "as leverage to enhance their sphere of influence throughout the Middle East,"^[i] perhaps by using Hezbollah, their Lebanese protégés, to turn up the heat against the Jewish state or to assert their claims over disputed areas of the Gulf Straits or Caspian Sea.

This argument is, however, fallacious because it exaggerates the role of nuclear weapons: half a century on, Liddell Hart's argument that a nuclear bomb deters only nuclear blackmail while conventional forces deter the attack of a conventional army remains unchallenged by experience. So as long as Israel maintains its overwhelming preponderance of non-nuclear firepower, an Iranian bomb will make no real difference to the behaviour of any conventional forces in the field.

Another argument, however, is that elites inside the Iranian regime can secretly pass fissile material along to its terrorist allies, whose fanaticism renders them immune from the mutually assured destruction that their use would invite. "What check is there that Iran would not transfer even some of its WMD technology to terrorists?" as Zalmay Khalilzad asked two years ago.

No one seriously disputes this is a cause for concern - as serious as the prospect of the Pakistani Inter-Services Intelligence passing its own nuclear materials into the hands of its proxy forces in Kashmir. But it is not, however, the paramount reason why an Iranian bomb really matters, because it is a threat the outside world can easily deter: if your protégés use Iranian weapons, the Iranians will still be accountable and must pay the price.

Nor is it enough to say that the development of an Iranian bomb would provoke a regional arms race that could prove highly destabilising, just as India's nuclear programme during and after the 1960s provoked a comparable Pakistani reaction. Iran's current situation differs considerably from the Indo-Pak model. Israel, its regional enemy, and Pakistan, a possible future rival for influence and resources, are already nuclear powers and the other countries that might feel threatened - Saudi Arabia, Iraq and Turkey - are already well-protected by the long arm of the American nuclear umbrella. With whom, then, is this arms race going to occur?

The most convincing reasons to be deeply concerned about an Iranian bomb are in fact the least mentioned. The first is that the development of a warhead would be seen by ordinary Iranians as a huge national achievement and thereby enormously boost the prestige of the current regime. If this helps to sustain the rule of the mullahs, then the cause of democracy and human rights inside Iran would be dealt a very hard blow.

Viewed in these terms, stopping the development of an Iranian bomb is one of the very few things the outside world can constructively do to assist the humanitarian cause. The decade-long efforts of the European Union to promote human rights inside Iran has achieved nothing, not least because anything that smacks of foreign interference immediately raises hackles and so becomes counter-productive. "The truth is that European Critical Dialogue has failed to deliver," as a senior Western diplomat told me in Tehran last autumn, admitting that the single supposed achievement of the policy - a moratorium on the stoning to death of some criminals - officially ended a practice that was already dead in practice. But we are not powerless to prevent the mullahs reaping a political harvest of nationalism when they successfully test-fire a nuclear device.

An Iranian bomb also matters because the possibility of serious political unrest inside Iran over the next few years cannot easily be discounted. It is of course possible that the mullahs will cling to power in the same way as the Chinese communists have clung to their own, buying off their enemies and introducing populist measures as well as ruthlessly suppressing disorder. But should the regime crumble before violent street protests, then the ensuing anarchy could easily allow nuclear materials to be spirited away by anyone who can bribe or steal their way into nuclear installations. And just as former Soviet and Iraqi scientists were headhunted when their own masters fell from power, so could destitute Iranian scientists one day also prove easy targets for foreign governments wanting their expertise.

Finally, the development of an Iranian nuclear bomb would reveal an alarming truth that bodes ill for the future: for all the formidable powers of intelligence gathering that lie at their disposal, and for all the immense weight of diplomatic and economic pressure that they can muster, the Western powers are ultimately unable to prevent a government from developing a nuclear warhead if it has sufficient determination and resources. So an Iranian warhead could conceivably prompt other governments to introduce or accelerate their own nuclear programmes - not to deter any threat from Iran, but because such a development could raise hopes that they, like the mullahs, can succeed in doing so.

There are, then, very good reasons to fear an Iranian bomb and hope that it does not become a reality.

Roger Howard is a British defense journalist and author of Iran in Crisis? (Zed Books, London & New York, June 2004 www.zedbooks.co.uk)

^[i] The Weekly Standard, 2 September 2002