The freed British sailors on Friday insisted that they were in "routine boarding operation" inside Iraqi waters at the time of the capture by the Iranian navy.
"I can clearly state we were 1.7 nautical miles from Iranian territorial waters," Royal Marine Captain Chris Air said at a press conference as he read a joint statement on behalf of the group.
According to the statement, they were told if they didnot admit they had strayed into Iranian waters they faced seven years in prison.
"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 were blindfolded, bound and subjected to random interrogation, and faced "constant psychological pressure", said the statement.
"We were blindfolded at all times and kept in isolation from each other...We were blindfolded, our hands were bound, we were forced up against a wall."
Seven of the 15 freed sailors attended 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, the 15 British sailors detained by Iran for nearly two weeks returned safely 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. And after seeing their families, they 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 would 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 the Iranians. And Qatar and Syria had played useful roles in the release of British navy personnel.
On March 23, the 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.