President Mahmoud Ahmadinejad dragged his rambling monologue out for two whole hours before dropping his verbal bombshell that Iran planned to release the 15 captured British marines and sailors as a “gift” to mark the Prophet’s birthday.

The announcement took Downing Street, the Foreign and Commonwealth Office and the Ministry of Defence completely by surprise.

British officials handling the crisis had noted a change in mood this week but no one imagined that the Iranians would climb down so quickly without demanding anything in return.

So what caused this sudden turn about?

Certainly Mr Ahmadinejad has not suddenly gone soft on the West. Most of his press conference yesterday was taken up with a diatribe against America and Britain, who were blamed for most of Iran’s historical setbacks and most of its current ills.

He also repeated the claim that the captured Britons had entered Iranian waters illegally. To reinforce the point he pinned a medal to the chest of the Iranian officer responsible for capturing them.

The only possible explanation is that the release was ordered by Ayatollah Ali Khamenei, Iran’s Supreme leader, who has so far not spoken publicly about the 13-day crisis.

Behind the scenes it is assumed that a fierce struggle has been taking place in Tehran between hardliners and pragmatists.

The extremists wanted to put the British on trial or at least hold them as a bargaining chip for the release of five Iranian officials arrested by US forces in Iraq in January who are still in custody.

The more moderate elements advised the opposite. Iran is already reeling from sanctions imposed by the United Nations Security Council and in all likelihood faces further measures this year if it is does not halt its controversial nuclear programme.

The British might not have been in a position to use force against Iran but they did demonstrate that they could muster powerful allies around the world willing to take up the cause of the captured British sailors and marines. Iran’s economy is already weak, further action could damage the Government’s power base.

The UN Security Council passed a resolution calling for an end to the crisis. A tougher worded statement came from the European Union. Key Middle East regional powers, like Turkey, Syria, Saudia Arabia and Iraq also took up the cause and bombarded Iranian leaders with calls to free the British.

Many leaders in the region feared that the incident could provide the spark for a new conflict in the Gulf. US forces have been massing in the area and there are genuine fears that President Bush may order an attack on Iran before he steps down from office..

Yesterday Tony Blair made it clear to the Iranians that he had two options available to him. One was patient diplomatic negotiations. Failling that he could squeeze Iran internationally, further isolate the country and set the stage for a prolonged conflict.

Amazingly, Iran blinked first and the crisis which threatened to destabilise the region further now looks to be over. The sailors and marines should be home to enjoy Easter with their families.

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