It is a diplomatic coup for those opposed to Iran’s nuclear ambitions to have managed to get such broad support for a third round of United Nations sanctions. The vote, of 14 members in favour, with only Indonesia abstaining, represented a triumph of bargaining over the past 72 hours and a clear rebuff to Iranian nuclear ambitions. Libya and South Africa accepted special wording making clear that Iran was being treated no differently from other signatories of the Nuclear NonProliferation Treaty.

The substance of the sanctions is slender but still represents a real advance on the previous two rounds. However, the most valuable aspect may be the timing, with Iran’s parliamentary elections less than two weeks away. It will be hard for President Ahmadinejad, at a time of rising food and fuel costs for the Iranian economy, to portray as helpful the new damage to its ties with the outside world.

David Miliband, the Foreign Secretary, said: “The world is not turning its back on Iran” and that the offer of “economic and scientific cooperation is still on the table” but that “the risk of an arms race in the Middle East is too great for us not to address”.

The most encouraging part of the negotiations to get the new Security Council resolution is the solidity of the “Euro-Three” – Britain, France and Germany – and the council’s other three permanent members, the US, Russia and China. Fears that Russia and China would veto the resolution fell away as they agreed to put their concerns about Iran’s ambitions above their desire for commercial and strategic links with Tehran. Miliband said: “The way in which [the six] held together has defeated the predictions of those who said the international community would blink.”

The second encouragement must be the clear warnings of the International Atomic Energy Agency. Mohamed ElBaradei emphasised his grave concerns at the possibility that Iran intends to give itself the capability to make nuclear weapons despite its denials.

The report by the UN’s nuclear watchdog last week contained the usual mixture of areas where the IAEA felt Iran had obstructed its inquiries and those where it felt satisfied. In the past, Iran has used the even-handedness of these reports to claim endorsement of its behaviour. But the IAEA’s tone, this week and last, has been distinctly more blunt in sounding the alarm.

This goes some way to mitigate the damaging effect of the US’s National Intelligence Estimate late last year, whose conclusion that Iran had abandoned the active design of nuclear warheads has been used by Tehran to imply that it is innocent of all charges.

As the IAEA has now emphasised, that is far from true; the actual design of a warhead is the easiest of the technical steps in acquiring that capability. Uranium enrichment is the real obstacle.

The new sanctions include a ban on dealings with two Iranian banks, travel restrictions on named Iranians and some detailed curbs on its exports. Judging by its reaction to past sanctions, and by the attention it has paid to these talks, Iran will talk tough but will find it hard entirely to shrug off the practical consequences of the bans or the wider warning that even supposed allies dislike its nuclear work. Iran’s highly controlled elections will not be a good test of what Iranians think of their leaders, let alone this single issue. But all the same, it will be hard for Ahmadinejad to portray more isolation as a help to Iranians at a difficult time.

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