Gordon Brown was right yesterday to threaten Iran with tougher sanctions immediately – if premature in announcing that the European Union had already formally agreed to do so, and if too grand in implying that freezing an Iranian bank’s assets was, on its own, a big step. It was unfortunate that his declaration, after meeting President Bush, was apparently contradicted by an EU spokeswoman for Javier Solana, the Union’s foreign policy chief.

Technically, that is right: the EU scheme to freeze the foreign assets of Bank Melli will take more days to sort out. But although Iran has an almost limitless capacity for reading only the messages it wants from international signals, in this case it would be wrong to brush away the threats. Brown is justified in asserting that EU members, and Russia and China, are more convinced than ever before of the urgency of leaning on Iran to curb its nuclear work. The problem is to turn that anxiety into real pressure. Iran has seen these banking curbs coming and will be able to evade much of the impact. The real task is to agree on ways of disrupting its import of petrol and export of oil and gas.

On Saturday Solana, together with political directors of the “E3 plus 3” – the US, Britain, France, Germany, Russia and China – pitched up in Tehran to present their best offer since the summer of 2006. But it wasn’t very different from that package of precise offers and vague threats which has failed, in two years, to stop Iran enriching uranium. Enrichment is the most difficult step in making a bomb, Iran’s presumed goal (although one that it still denies). Asked what was better now, a senior British official said that the passage of time made a difference. “They are now in a position where they recognise that we are serious.”

Maybe. The weak point of that argument is that oil is now nearly $140 a barrel, more than double its level two years ago. Bush leaves office soon. And in the past two years the divisions among those countries discussing sanctions have been advertised. China and Russia, both permanent members of the United Nations Security Council, whose support is needed for UN sanctions, are keen to keep commercial ties with Tehran and have only recently been nudged into alarm at the thought of its nuclear weapons. Germany (and come to that, Italy), also with strong ties, have got in the way of a joint European position as tough as Britain and France wanted.

But Iran’s economic predicament has worsened, given its need to import petrol, the vulnerability of its poorest people to rising food prices and its failure to develop other sources of income. Those pressures, and the handling of the nuclear programme itself, have caused rifts within the regime (although high hopes of this have come to nothing in the past).

It is the right point to toughen sanctions farther, and to look at curbs on oil and gas trade. The US Congress, for one, has found agreement on this elusive in the past, partly for fear of disrupting the markets more and sending prices higher. Nor has anyone wanted to pick a fight with Iran when incentives seemed to have a chance. But Iran’s dismissive response this weekend suggests that the high-profile petition has got nowhere. Better to pick a fight when Iran’s worst weapon is still just oil.

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