The detained sailors and Marines are likely to be kept in good physical conditions but will find their detention by Iranian forces a frightening experience, experts say.

The 15 are most probably being held in the military barracks at Jamshidiyeh in the foothills of the Alborz mountains which shelter Tehran. Although the seven Royal Marines are drilled in techniques to cope with capture, the eight sailors have little relevant training.

The number of vehicles entering the barracks has increased significantly since the British were caught, according to Alire-za Nourizadeh, a senior researcher at the Centre for Arab--Iranian Studies in London.

The complex has an iconic role in Iranian revolutionary history and is no stranger to unwilling VIP guests. The Shah of Iran’s former officials, including a Mayor of Tehran, cabinet ministers and the Empress’s bureau chief, were locked up there in the 1970s.

“They are kept in rooms with heating and [air] conditioning,” Dr Nourizadeh said. “They are getting good food and will be allowed to watch the television for a few hours each day and the guards will try to get them newspapers.

“They will be scared. They will feel under pressure because they will hear chants of ‘Death to America, death to the UK’ [from soldiers in the barracks]. They will see men with guns. They will see all sorts of threatening gestures from the guards and the people around them will look at them with hate in their eyes.

“They [the leadership of the Revolutionary Guards] wanted to show to the Iranian people that they are so strong that they can go and take British troops. They wanted to keep these soldiers for some time and see what happens.

“Now they will want to show the Iranian people that they are not going to give in to British demands.”

A Ministry of Defence source said that the sailors being held would have been given little training in how to cope with capture. “The sailors would probably have watched a video followed by a question-and-answer session,” he said.

“The Royal Marines would be better prepared. The key of their training is to keep themselves alive and to deny any intelligence to the enemy. They would be aware of the psychological and intelligence tricks that would be used against them.”

Videos of the captives have shown them eating kebabs and smoking. They have been seen smiling and looking relaxed.

What is happening off-screen is a matter of constant concern in London. Iran’s refusal to grant consular access to the prisoners is alarming. The Revolutionary Guards’ erratic record feeds Britain’s fears.

The Guards, a corps established after the 1979 revolution to protect the fledgeling Islamic republic from “internal and external threats”, is the regime’s most trusted power centre when it comes to national security and has every reason to humiliate “little Satan” Britain.

Iran is expected to make a training film about the Britons’ detention as it did when eight British sailors and Marines were seized briefly in similar circumstances in 2004.

That video, being shown in selected universities to students of the Baseej, a hardline civil defence force, portrays the infidels as powerless in the face of devout Iranian forces. One of the Britons had “wet his pants” when a Revolutionary Guard yelled at him, Soheil Karimi, the film’s director, told students at the film’s premiere in November.

Chris Adams, a navy reservist from the 2004 incident, told the Plymouth Evening Herald how the Iranians had removed the two senior officers from the rest of the men. The Britons were moved around in twos to reduce the likelihood of an attempted escape. The 15 sailors and Marines now being held are believed to include an officer but it is unclear if he is with the rest of the party.

“They took everything from us and blindfolded us,” Mr Adams said. “I was scared. We were blindfolded and had weapons pointing at us. We were not allowed to talk.”

As now, the Iranians insisted that the Britons were in their waters although the captives were convinced of their innocence. The British decided to humour the Revolutionary Guards.

“It was pretty rough and ready. We were pushed about. They kept asking us why we were in Iranian waters,” Mr Adams said.

“When we were briefed we were told that, as we were not at war, we could tell them what we needed to survive.

“We told them we were very sorry for being in Iranian waters — we were prepared to tell them anything they wanted to hear.”

He continued: “We were given an adequate amount of water. We were drinking out of a bucket, eating our food off the floor but you eat. We didn’t question it. It was 55 degrees.”

If Iran decides to try them for illegal entry they will come under the control of the hardline judiciary.

There is virtually no precedent but diplomats say that the legal procedure could take two different courses. In one the Britons could face a judicial administrative procedure rather than a trial in its usual sense with argumentation and barristers. A judge or the prosecutor would record the facts and either then, or after a recess, the judge would give his decision. Britain would not necessarily be informed in advance of the proceedings.

Alternately, the authorities could give notice of a trial, in which case British diplomats would ask to be present and the detained Britons might have a lawyer to speak for them. In either case, the proceedings would be swift, amounting to summary justice.

A long week

Friday, March 23 Iran seizes 15 Royal Navy sailors and marines in Gulf. British and Iranian envoys are each summoned to host foreign ministry

Saturday Iran says sailors have confessed to entering Iranian waters illegally. Britain repeats calls for their immediate release

Sunday Margaret Beckett speaks to Iran counterpart. Tony Blair calls for release of captives. Iran says it may pursue illegal entry charges

Monday Iran tells Britain detainees “fit and well”. Faye Turney, 26, naval boat driver, named as a captive

Tuesday Tony Blair gives warning of “different phase” if sailors not freed; shows Iran data that the 15 were in Iraqi waters. US Navy begins biggest Gulf exercise since 2003 Iraq invasion

Wednesday Britain publishes GPS coordinates of navy team and freezes all other diplomatic business with Iran. TV in Iran shows captives. Letter “from Turney” published saying Britons were in Iranian territory. Britain expresses outrage at video and letter

Thursday UN issues statement, not as strong as Britain sought, expressing “grave concern”

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