In one sense it is perhaps just as well that it was British, rather than American, sailors and marines who were taken prisoner. If they had been Americans, the rump of neoconservatives in the Bush administration, in particular Dick Cheney and Elliott Abrams, would have been saying: "We told you so." They have long argued that Iran is not susceptible to diplomatic pressure, that the European approach is doomed to failure and the only way to stop Iran acquiring a nuclear-weapons capability is a military strike on its nuclear facilities.

Even though the prisoners are British rather than Americans, neocons have been desperate to head for television studios. The only reason they have not done so yet is a request by the British government to the Bush administration to stay out of it. Word has also reached members of Congress. The British fear is that even a mild rebuke from President George Bush, or a neoconservative such as John Bolton, will be counterproductive, escalating the crisis and making it harder to get the 15 back.

Tony Blair is well aware of the battle lines in Washington and, hopefully, will keep this at the top of his mind during the crisis. He is in a hard place this weekend. He is, understandably, under pressure from the public and parliament to do something amid a sense of outrage that Iran not only captured the group, but denied them consular access and paraded them on television. To address these concerns Mr Blair has made the necessary strident noises.

But he has to resist more hysterial voices. Throughout his premiership the British government has consistently opted for negotiation with Iran to try to resolve the nuclear issue, not military action. And now, after years in which the US refused to participate, the British government has serious allies in Washington. The US secretary of state, Condoleezza Rice, and the defence secretary, Robert Gates, are pursuing engagement and are prepared to talk to Tehran. The duo are in the ascendancy in Washington while the Cheney-Abrams alliance is temporarily relegated to the sidelines. Ms Rice and Mr Gates think their approach is working, that there are signs of anxiety in Tehran over sanctions and other economic measures, as well as the diplomatic pressure. They argue that Iran is not like North Korea, and that it does not want to be isolated.

How Mr Blair handles the present crisis could crucially impact on this internal Washington debate. Mr Blair has options. The prime minister, who has a genuine dislike of and concern about the Iranian president, Mahmoud Ahmadinejad, could still ask Washington to set the drums beating. That would suit Mr Cheney and Mr Abrams. At this stage such an approach, thankfully, seems unlikely.

Alternatively Mr Blair could have opted for a quieter approach, choosing discreet, bilateral discussions, but was advised that this would not work. Instead he has opted for a middle route, internationalising the crisis, seeking the help of other countries to put pressure on Tehran. Countries in Europe and the Middle East have been helpful: the United Nations security council less so.

Servicemen taken by Iran in 2004 were quickly released. The background is tenser now. Iran's Revolutionary Guard, which is holding the 15, has suffered a series of setbacks in recent months, from the capture of six members of its Quds brigade in Iraq through to the defection of a senior commander to the west. British pressure applied through its allies may not have much impact on the Revolutionary Guard, but it will influence the foreign ministry and perhaps even Iran's supreme leader, Ayatollah Ali Khamenei.

It could take a while for Britain to secure the release of the sailors and marines. In the meantime Mr Blair has to placate the British public. But he must also show patience and do nothing that will undermine Ms Rice and Mr Gates.