Iran will stop exporting fuel oil in the New Year, officials announced yesterday. It needs it for its own people. That is a measure of how the plunge in oil prices from $140 a barrel to $40 is hurting the world’s fourth-largest oil exporter. Is this the shock that might nudge Iran’s leaders to think again about their nuclear ambitions? To be blunt, probably not. Nothing so far has made them budge from the goal of enriching uranium in a way which would put a nuclear weapon within reach.

All the same, the sharp fall in the oil price, coming at a crucial stage in Iran’s nuclear work, does strengthen diplomatic efforts to dissuade the Tehran Government. It may even topple that Government. Those who have been trying – and failing – to persuade Iran to change direction now wonder whether the sudden shock of plunging national income might persuade Iranians to pick a new president in the June elections. Mahmoud Ahmadinejad’s promise to put oil money on the tables of Iran’s poorest people – a slogan which people were delighted to interpret entirely literally – won him the presidency in a shock result in August 2005. But by last summer, many were grumbling that he had failed. Now, the oil money has run short as well.

Last week the president acknowledged for the first time, through the official IRNA news agency, that the Government will have to cut spending and subsidies for food and fuel, as well as raise taxes. He added that the budget would have to cope with oil at between $30 and $35 a barrel. Analysts reckon the budget last year was based on oil at about $90 and even this year a balanced budget appeared to require oil at around $60 a barrel. A new president in Iran – as well as one in the US – would allow a new attempt to see whether Iran is open to a deal. The best that can be said of the incoherent and constantly-changing mix of sanctions, vague military threats and trade inducements which the US and Europe have lobbed at Tehran for six years is that they have left the Iranian leadership unclear about what those countries are prepared to do to stop the nuclear work and so, arguably, more cautious.

Barack Obama tied himself in knots early in his campaign about whether he would talk to Iran. His first answer – broadly, yes – was his best. For the US not to have relations of any sort with Iran is self-defeating.

One of the least productive reflexes of US foreign policy has been to regard the granting of contact with American officials as a prize in itself, not a means to an end. All the same, Obama will need to devise some kind of technical contact to explore a deal that could not be portrayed as a prize.

It may still not work. Much of the current analysis of how to deal with Iran’s nuclear work (such as an excellent report by Mark Fitzpatrick of the International Institute of Strategic Studies in London) focuses on how to persuade it not to make enriched uranium into a bomb. It acknowledges that Iran is nearly there.

But, for the first time in the six years since Iran’s secret nuclear work was exposed, the Government may want trade with other countries and a solid prospect of affluence for its people even more than it wants to boast of nuclear success.

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