The two faces of Tehran: how diplomats and extremists fight for control of foreign policy

Iran proudly boasts of its 3,000-year history, but its behaviour is more like that of a dysfunctional family when it comes to its international relations.

Last night's dramatic footage demonstrates how extremists with a grudge against the West and a burning sense of ambition can force Iran into sudden confrontations that its smoothest-talking diplomats can have trouble defusing. The revolutionary guardsmen and their radical supporters behind this crisis only represent a single faction, but they have been able to take Iran's foreign policy hostage and provoke an international incident.

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Taking advantage of the deep fractures in the Iranian state, the revolutionary guards have created a fait accompli, forcing the government to adopt a position from which it will be hard to back down. Driven by their experiences of the revolution and eight bloody years of war with Iraq, many guardsmen want to see Iran take a more aggressive stance against Britain and America.

The confusion is caused by Iran's unusual political system, which combines democratic elements such as an elected president and parliament with the theocratic rule of a supreme leader. In practice, this means decisions are rarely made by a single person: they are disputed and fought over by a host of political factions and vested interests including religious leaders, elected politicians, wealthy merchants - and soldiers.

Analysts believe the latest confrontation stemmed from a desire to show Britain and America that Iran can hit back despite coming under sanction for its nuclear programme and having military figures arrested in Iraq. Revolutionary guards and their supporters in government have always viewed the occupations in Iraq and Afghanistan with the deepest suspicion and accuse America and Britain of fomenting unrest among their own ethnic minorities.

Last night the footage of Faye Turney was only being shown on Al Alam, an obscure satellite channel with close links to the Revolutionary Guards. Because it only broadcasts in Arabic rather than Persian, few Iranians would have seen the footage, suggesting there is still much opposition to escalating the crisis.

Because of a protracted new year holiday, there have been no newspapers available in Iran for more than a week. Analysts say this media blackout is because top regime leaders do not want to back themselves into a corner by making inflammatory statements or promising particular courses of action. There is some speculation that the decision to air last night's footage came in retaliation for Britain's decision to stop all diplomatic business unconnected with the case.

The big question is whether the guards had had authorisation to capture the boats and show the film from the Supreme Leader, Ayatollah Ali Khamenei. Last week the leader made an unusually strident speech promising to stand up to Iran's "enemies", which could have been loosely interpreted as a green light to act against British forces who came too close to Iranian waters.

Hardline groups, including student members of the Basij Islamic militia, which falls under the aegis of the revolutionary guards, have demanded that the Royal Navy personnel be put on trial. That view is supported by hardliners who want to send Britain a message that its presence in Iraq and tough line on the nuclear issue could have unpleasant consequences.