Katherine Butler: Iran has rarely been less likely to do favours for Western powers

David Miliband sounded positive as he expressed the hope last night that the detention of a yachtload of British sailors by Iran would be "resolved swiftly". The families of the hapless yachtsmen will have to pray the Foreign Secretary's words are based on more than wishful thinking. Because Iran has rarely been in less of a mood to do favours for any Western power, let alone Britain, the country which arouses most suspicion in the minds of its leaders.

This incident has all the makings of the latest protracted crisis between Iran and the West in which the five yachtsmen could become pawns. Clearly these sailors are not naval personnel, and Mr Miliband will be doing everything to reassure Tehran that they strayed innocently into Iranian waters. On the face of it, there is tactically little for Iran to gain, even in its deepening nuclear stand-off with the West, by holding them for more than a few days.

By last night, it was still not clear if Iran had accused the men of spying or any other misdeeds. The hopeful scenario is that they will be freed in a gesture of magnanimity, sent on their way in a blaze of handshakes and photographs, perhaps even dressed in identical Iranian-made suits, just like the eight British naval personnel arrested by Iran in 2007, and eventually freed as "a gift" to the UK.

But there are several recent precedents to suggest a more ominous outcome. Three American hikers strayed over the Iraqi border into Iran earlier this year apparently while on a trekking holiday. They were seized, taken to Tehran and are now facing trial for espionage. A few months before them, Roxana Saberi, a young American-Iranian journalist was convicted of spying and sent to jail for eight years, although she was eventually freed.

Ali Ansari, professor of Iranian history at St Andrews University believes much will hang on the fact that the yachtsmen's fate will be decided by just two men: Iran's Supreme Leader Ayatollah Ali Khamanei and his close ally, the hard-line President Mahmoud Ahmadinejad. Neither is remotely interested in mollifying the West.

Indeed, since the disputed June elections which returned Mr Ahmadinejad to power, events inside the country have put this axis hugely on the defensive. The Supreme Leader and the President are waging a power struggle with clerical and reformist factions who accuse them of betraying the ideals of the Islamic revolution. They are also engaged in a brutal suppression of groups and individuals who organised the post-election street demonstrations, the biggest show of opposition since the 1979 revolution. Did the five-man yachting crew play (or sail) directly into the regime's hands, presenting the perfect "crisis" from abroad they can exploit?

As Dr Ansari says: "My guess is they will hang on to them because it will help divert attention domestically and also divert the foreign media from demonstrations planned for 7 December. There is always method to their madness."