Body language experts said last night that there were obvious contradictions between the upbeat tone of Faye Turney’s words and her appearance.

Although during the short clip released by the Iranian authorities Ms Turney praises her “friendly, hospitable and thoughtful” captors, there were signs of her anxiety at the situation, one said.

Robert Phipps said a faint smile that appeared to play across Ms Turney’s face at one point told a thousand words.

“It was a fixed no-teeth smile,” he said. “When you are being genuine there is a muscle in the face, the zygomatic muscle, which forces the corners of the mouth to turn up towards the eyes. There is an equivalent muscle in the eye, the orbicularis oculii muscle, which brings the corners of the eyes down towards the lips.

“You can’t make these two muscles work unless you have genuine warmth and happiness. This was a forced smile, which is for other people.”

He added: “Her speech was very slow and monotonous, she has furrowed eyebrows and her eyes were downcast to the right, which shows she is going into her emotional channels.

“She blows the smoke down which shows she is feeling negative and lacking confidence. She is obviously very stressed.”

The incongruous image of Ms Turney clad in a headscarf while smoking, which is generally frowned upon in Islamic societies, may have been to colour the perception of the captives within Iranian society. Ms Turney, 26, is also seen smoking on board a boat shortly after her party of marines were captured last Friday.

The footage of Ms Turney and her fellow marines eating was in stark contrast to the far more intimidating pictures of the eight marines and soldiers who were seized in June 2004 by the Iranians. This group, who were released after three days following an admission that they had strayed into Iranian waters, were paraded blindfolded in footage released by the Tehran Government. The soldiers later said that their captors had staged mock executions and accused them of espionage.

Ms Turney’s group are seen eating. Only a handful of faces are seen: one close-cropped sandy-haired male and another two brown-haired males. All appear fit and well.

Ms Turney says in a letter that they are being fed three times a day and given plenty of fluid.

“They explained to us why we had been arrested. There was no aggression, no hurt, no harm. They were very, very compassionate,” she said.

Her patrol boat had “obviously” trespassed into Iranian waters, she said, but they were being treated well by their “friendly, hospitable, thoughtful and nice” captors.

The letter, apparently written by Ms Turney, was released simultaneously by the Iranian authorities. In it she says she has written to the Iranian people to apologise for “apparently” entering their waters.

She writes of her hope of being released for her daughter Molly’s birthday party.

Crisis options

1. Continue diplomatic efforts Pressurise Iran through third parties. Be prepared to apologise and see British Forces humiliated on television. Hope to secure freedom in similar manner to release of Britons held three years ago

2. Increase pressure on Iran Suspend bilateral ties. Step up rhetoric. Prepare ground for taking action through European Unionand United Nations. Hope pressure results in climbdown.

3. Press for sanctions Build on efforts at UN against Iran’s nuclear programme by further isolating Tehran. Aim to hurt already fragile Iranian economy.

4. Break relations Expel Iranian diplomats and other officials from London. Withdraw British diplomats from Tehran. Press for punitive action, such as sanctions against regime in every international forum.

5. Military option Send special forces into Iran to rescue British Forces. Boost troop levels in southern Iraq to counter Iranian influence. Make it clear that seizure of British Forces was an act of international piracy.

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