Iran’s brinkmanship has entered a new and potentially dangerous phase. The 15 Royal Navy personnel captured on Friday were moved to Tehran yesterday, presumably for propaganda purposes. So far, calls for their safe return by Margaret Beckett, the foreign secretary, have fallen on deaf ears, as have her demands for a full explanation from Tehran.

Mahmoud Ahmadinejad, Iran’s president, is playing an obvious game. Last night the United Nations security council was voting in New York on extending sanctions against Iran, banning arms exports and freezing assets of individuals and companies involved in its nuclear and weapons programmes. The security council tested the water with limited sanctions in December. Last night’s vote was aimed at ratcheting up the pressure.

Welcome muscle is coming from other quarters, too. Russia is reported to have issued an ultimatum threatening not to supply fuel to Iran’s Bushehr nuclear power plant unless it suspends its uranium enrichment programme. Moscow is also said to be withdrawing its engineers from the plant, concerned at the prospect of a nuclear-armed Iran. Now Iran’s state-run media have accused Russia of being an “unreliable partner”.

In Iraq, meanwhile, both America and Britain have gone public by accusing Iran of arming and funding Shi’ite militia groups. Dick Cheney, the US vice-president, has said that Iran is “fishing in troubled waters” by supplying and providing suc-cour to the insurgents. From Tehran’s perspective things look rather different; four years of what it would see as postinvasion chaos have provided it with a tremendous opportunity to settle old scores and exert its regional influence.

Mr Ahmadinejad, once a member of Iran’s Revolutionary Guard, responds in the way you would expect from a man with that pedigree: he sees attack as the best form of defence. Last week we reported an article in Subhi Sadek, the Revolutionary Guard’s weekly paper, which talked of capturing “a nice bunch of blue-eyed blond-haired officers and feed them to our fighting cocks”.

Britain, with an outgoing prime minister who has effectively said military action against Iran is not an option, looks the weakest link. Iran would probably not have seized American soldiers, even on the pretext that they had strayed into its territorial waters. When Iran seized British personnel three years ago, they were paraded in blindfolds and made to apologise before being released. A similar stunt may be planned this time.

What is self-evident is that Iran is continuing to defy the UN by proceeding with its nuclear programme, testing missiles and fuelling the insurgency in Iraq. One hope is that the political tide will turn against Mr Ahmadinejad in favour of Ali Akbar Hashemi Rafsanjani, the former president, or the younger generation of political reformers. But if Ayatollah Sayyid Ali Khameini, the country’s supreme leader, is an accurate weather vane, it would be unwise to rely on anything happening soon. His recent speeches have tended to back his president’s belligerent approach.

What keeps Mr Ahmadinejad guessing is how Israel and America will respond. The Israeli military, as we reported recently, has been conducting dummy runs for targeted strikes against Iranian nuclear facilities, using the model of its successful attack on Iraq’s Osirak reactor more than a quarter of a century ago. Israel has made it plain that it cannot coexist with a nuclear Iran. America, too, has beefed up its military presence in the Gulf. With men like Mr Cheney around, George Bush’s apparent determination not to leave the White House with unfinished business in Iran carries weight. What that means is uncertain, although a recent European Union poll surprisingly shows most people favour using all means, including force, to stop Iran getting nuclear weapons. Mr Ahmadinejad’s diversionary tactics should be seen for what they are. Keeping up the pressure on Iran is paramount.