'The dog returns to its vomit, and the sow returns to her mire/ And the burnt fool's bandaged finger goes wabbling back to the fire." Kipling was right. Britain is out of Iraq and desperate to get out of Afghanistan. So why gird ourselves for a fight with Iran, a proud country of 75 million people with whom we cannot go to war without taking leave of our senses?

Do any of Britain's leaders really think further economic sanctions will stop Iran's nuclear programme? I cannot believe it. Sanctions did not topple Saddam Hussein, Slobodan Milosevic or Muammar Gaddafi; they led merely to war. Sanctions have been imposed on Iran for 33 years because there was nothing else to do. They have done no good and almost certainly been counterproductive in reinforcing autocracy.

Washington has announced new commercial and financial sanctions on Iran, blacklisting anyone who does business with it. With an election in the offing, President Obama must show America's pro-Israel lobby that he is tough somewhere in the Middle East. The EU must this month decide whether to collude with the US in this dangerous game and ban Iran's oil exports. The threat was enough to get Tehran to test medium-range missiles in the Gulf, and its wilder heads to murmur about closing the Straits of Hormuz, thus blocking a third of the world's sea-borne oil.

This sabre-rattling – in the midst of a recession – is beyond stupid. No one has seriously doubted that Iran's government, surrounded by nuclear-armed or nuclear-allied powers, would one day seek a similar capability. It is the nature of well-resourced and insecure regimes to find comfort in "the ultimate weapon". It seems of no account that no war fought by a nuclear power has seen such a weapon even threatened. It was not a factor in Korea, Vietnam, the Falklands, the Caucasus, Kashmir or numerous Middle East conflicts. The one time such weapons were "on the table" was over Cuba in 1962 – and then they probably helped prevent war.

Any fool may say, you cannot be too careful. It is the motto of the arms race. Israel has a nuclear capability for that reason, and that is why Iran wants one. A pre-emptive Israeli strike on Iran's nuclear plants might postpone their work, but make eventual war more likely. I would prefer it if Iran had no such missiles, but that is hardly for Britain to say when it demands "the right" to its own. In this case, what matters is the avoidance of escalation, of the megaphone belligerence that makes some western leaders vulnerable to the "inevitability" of war.

The only question for the west over the last three decades has been how to respond to Iran's fundamentalist leadership and, more recently, its craving for nuclear status. The answer has been of startling ineptitude. The attempt to set up pro-west regimes in Iraq and Afghanistan led the west to upset the balance of power established by the Iran-Iraq war and the Taliban-Pakistan regime in Kabul. Now the Iraq occupation has secured for Tehran unprecedented influence in Baghdad. Its influence also penetrates deep into western Afghanistan, and its support for resistance movements in the Gulf sheikhdoms is said to be growing by the year. Where now the Foreign Office's famed Arabists?

The long experience of sanctions indicates that they suck the sanctioning powers into confrontation. Their imposition is a prelude either to inert hostility or to war. They embattle the victim regime, driving power and money to its ruling cadres. In Tehran, as in Tripoli and Baghdad in the 1990s, sanctions toppled nobody but made rulers and generals rich. They impoverish not just the poor but the mercantile and professional classes, denying them contact with the outside world. They hasten middle-class emigration and thus reduce the scope for political pluralism and opposition.

Government sources at the weekend rejected all this experience. They claimed tougher sanctions would "hasten Iran's economic collapse and deepen rifts within the regime, in the hope that saner voices will deem the price of pursuing nuclear weapons too high". This commits the democratic fallacy that totalitarian states react to economic pressure as democracies might. Sanctions do not initiate such a process. They just build walls. Meanwhile we are enraging Iran's scientific community by apparently condoning secret assassination as a way of impeding its nuclear programme.

The idea that any nation becomes more malleable when threatened from outside is absurd. A reasonable observer could assume that every utterance from Washington and London at present is scripted to bolster the Iranian leader, Mahmoud Ahmadinejad, on his insecure throne. The west's threats must exhilarate the young bloods of the Revolutionary Guard and depress the opposition. They may be supported by Iran's émigrés, but the diaspora is seldom a reliable guide to politics in the home country.

Economic sanctions are coward's diplomacy. They purport to high moral stance but are merely a low-risk way of bullying the world. The danger is that they encourage militarist lobbies to escalate the steps that lead to open conflict.

Those who argue against unnecessary war are routinely asked the father's knee question, "So what would you do?" Taught since 1939 that Britain must be seen to do something, the British are programmed to meddle. There have been occasions in the last 50 years when it has been right to declare hostilities against other nations – the Falklands, Kosovo and the first Iraq war. But usually the answer to "what to do" about foreign regimes of which we disapprove is, quite simply, to do nothing.

For the most part, other nations' business is not ours. In the last 25 years Britain has mostly been useless at putting the world to rights – it has struggled to wrap itself in the tattered flag of empire, at vast expense but to little effect. It would have been better, far better, to maintain good relations with other states in the hope of assisting causes we profess to hold dear. As for rattling a sabre whenever Washington says so, that is the most humiliating idiocy.