The 15 British sailors freed by Iran on Friday said they were subjected to "constant psychological pressure" and threatened with imprisonment during their 14 days ordeal in captivity.

They were told if they did not admit they had strayed into Iranian waters they faced seven years in prison, Royal Marine Captain Chris Air and naval Lieutenant Feliz Carman said in a joint statement at a new conference on behalf of the freed group.

"We were interrogated most nights and given two options. If we admitted that we had strayed, we would be back on a plane to the UK pretty soon. If we didn't, we faced up to seven years in prison," the statement said.

They said that they all were kept in "isolation" and in "stone cells" for most of the captivity in Iran.

"We were kept in isolation until the last few nights when we were allowed to gather for a few hours together, in the full glare of Iranian media." said they.

According to the statement, the freed group insisted that they were in "routine boarding operation" inside Iraqi waters at the time of the capture.

At the press conference, Royal Marine Captain Chris Air also defended why the group allowed themselves to be taken too easily at the time of capture, and be shown by Iranians on television.

"We were not prepared to fight a heavily armed force who it is our impression came out deliberately into Iraqi waters to take us prisoner .... They had come with a clear purpose and were never going to leave without us," said he.

"By the time the true intent of the Iranians had become apparent - and we could have legitimately fought back - it was too late for action," he said.

The day after 15 sailors safely returned the UK, six of the 15 freed sailors had a news conference in Royal Marine Base Chivenor in Devon, southwest England, issued a joint statement about their capture in the northern Gulf and subsequent detention.

On Thursday, 15 British sailors detained by Iran for nearly two weeks flew back to the UK, and reunited with their families.

After arriving at London's Heathrow Airport at midday, the personnel, eight from the Royal Navy and seven from the Royal Marines, then flew in two Royal Navy Sea King helicopters to Royal Marine Base Chivenor in Devon, southwest England, where they met their families, will have medicals and undergo a debriefing.

The debrief would last for "hours, not days" depending on "what their needs are," according to a Royal Navy spokesman.

Iranian President Mahmoud Ahmadinejad on Wednesday afternoon announced that Iran will free the British sailors later that day.

The announcement came moments after the president honored the Iranian coast guards who intercepted the British "trespassers."

It is not clear what prompted Iran to release the sailors and whether it involved some kind of deal.

According to Sky News reports, the British government had made no deal with Iran to secure the personnel and was in dialogue, not negotiations, with Iranians. And Qatar and Syria had played useful roles in the release of British navy personnel.

On March 23, 15 British naval personnel were seized by Iranian forces when they were patrolling off the Iraqi borders. Iran has insisted that the British boats illegally entered its territorial waters, while Britain said its soldiers were in Iraqi territorial waters.