Geoffrey Howe's resignation speech of November 1990 tends to be remembered for his lament on negotiating for Britain in Europe: "It is rather like sending your opening batsmen to the crease, only for them to find, as the first balls are being bowled, that their bats have been broken before the game by the team captain."

Last week, the US Congress attempted to break its captain's bat before a very important innings. Thirty two senators from both parties introduced a resolution to rule out "any policy that would rely on containment as an option in response to the Iranian nuclear threat". Closer to home, British foreign secretary William Hague echoed the logic. A nuclear Iran would spark off "the most serious round of nuclear proliferation since nuclear weapons were invented". It would result in "a new cold war in the Middle East" lacking all the "safety mechanisms" of the US-Soviet rivalry.

Comments like these reflect a growing nuclear alarmism that could drag us into an unwinnable and unnecessary war. A nuclear Iran is profoundly undesirable – but it's also eminently containable.

The first argument, that Iran is too crazy to be deterred, is historically untenable. Stalin's Soviet Union was viewed in exactly the same terms. NSC-68, one of the most famous American intelligence assessments of the cold war, judged Moscow to be "animated by a new fanatic faith, antithetical to our own", aimed at "domination of the Eurasian landmass". That was the year after the Soviets' first nuclear test. Mao Zedong, who was to acquire a bomb shortly thereafter, welcomed a nuclear war in which "imperialism would be razed to the ground, and the whole world would become socialist".

Senator Joseph Lieberman last week fumed that "containment might have been viable for the Soviet Union during the cold war, but it's not going to work with the current fanatical Islamist regime in Tehran". Well, fanaticism has pedigree. Stalin and Mao might have been bloodthirsty fanatics, but they were not suicidal. Nor is Mahmoud Ahmadinejad.

Last week, two of America's top intelligence officials told a senate hearing two important things. First, any Iranian decision to build a nuclear weapon would be based "on a cost-benefit analysis". Even fanatical theocracies are governed by reason. Second, "Iran is unlikely to initiate or intentionally provoke a conflict". If Iran is deemed to be unlikely to start a conventional war, it's not going to start a nuclear war.

And there's a simple reason for this. The area around Tehran contains a fifth of Iran's population, and half of the country's industry. A single Israeli thermonuclear bomb would wipe this out in the blink of an eye. Iran's abhorrent calls to wipe Israel off the map are gestures as empty as Mao's nuclear posturing.

Even if Iran is not crazy enough to use a bomb, wouldn't it encourage brinksmanship in one of the most sensitive parts of the world? Hasn't Pakistan been emboldened by its own nuclear shield to ramp up support for militants in Afghanistan and India?

One important distinction is that Pakistan hosts militants on its own soil, whereas Iran largely helps them "off-site", in places like Lebanon and Palestine. India can't attack Lashkar-e-Taiba, responsible for the Mumbai attacks, without attacking Pakistan itself. Israel, by contrast, will continue to be able to strike at Hezbollah or Hamas regardless of Iran's nuclear status.

The second argument concerns safety. The implication here is that a tinpot republic like Iran can't possibly be trusted to look after something so powerful. For a start, this misses the point that nuclear weapons are not like pregnancy – you can be a little bit nuclear. As James Clapper, US Director of National Intelligence, put it last month, Iran – much like Japan – is "keeping open the option to develop nuclear weapons" rather than putting together a bomb and attaching it to a missile.

If Tehran did put together a bomb, it might not be deployed. Iran, a large country with substantial conventional strength, has strategic depth. It can wait for threats to develop before, say, mating warheads to missiles. Apartheid-era South Africa, for instance, built a handful of nuclear weapons, kept them stored unassembled in a vault, and eventually dismantled them.

India, for a decade after its first nuclear test, didn't even bother to prepare a bomb. When it eventually did, neither it nor Pakistan meaningfully deployed their weapons for another 10 years. The two countries have since defied William Hague's suggestion that emerging nuclear powers can't implement safety mechanisms.

The third and final charge is that Iranian nuclear advances would set in motion a uncontrolled proliferation cascade as other regional powers scrambled for their own bombs. Yet history suggests that nukes don't inevitably beget nukes. A declassified American document from 1964, the year China went nuclear, identified over a dozen nations "with the capacity to go nuclear" – yet only a tiny fraction ever did. When the Soviets got the bomb, Yugoslavia or Sweden – both on that list of proliferating risks – did not follow. Taiwan did not follow China. South Korea and Japan did not follow North Korea.

The obvious retort is that all of these states were allies or clients of the US – but so too are Iran's rivals today. There are technical and political challenges to bringing Saudi Arabia, Egypt and Turkey under the American nuclear umbrella – but these are lesser problems when compared with the consequences of a military strike on Iran.

The alarmist response to Iran's nuclear programme reflects a failure of imagination and ignorance of history. Iran has an obligation to the International Atomic Energy Agency and the United Nations to explain the possible military dimensions of its nuclear programme. But if we – like the senators who sought to tie their president's hand last week – fool ourselves into thinking that a nuclear Iran cannot be contained, we increasingly back ourselves into a corner from which we will eventually be able to do little but lash out.

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