One of a group of British servicemen detained by Iran for three days in 2004 said he was "concerned" about the 15 currently being held.
The men captured in 2004 were paraded on Iranian TV
Christopher Adams, who was seized with seven others, after allegedly straying into Iranian waters, said it was a "very scary" experience.
He said they were given food and water, but told of a terrifying mock execution they were subjected to in the desert.
"We were in our cell, then we were moved out on to transport, blindfolded, driven around," he said.
"Then we got off, still blindfolded, told not to do anything or say anything. Told to put our hands on our heads then on the shoulders of the guy in front.
"We walked slowly into the desert and down into a ditch where we stood and waited to see what would happen.
"Thankfully they didn't fire. We didn't know what was going to happen. We thought there was a good chance we could have been shot then."
Mr Adams was detained after three British patrol boats were said to have passed into the Iranian side of the Shatt al Arab waterway in July 2004.
The six Royal Marines and two Royal Navy sailors were paraded on Iranian TV wearing blindfolds during their three days in detention. They were also filmed making an apology.
The servicemen were released in 2004 after three days
The seizing of the personnel and their boats, which have never been returned, sparked a tense diplomatic stand off.
The then Defence Secretary Geoff Hoon said the crews were "forcibly escorted" into Iranian waters.
Iranian Foreign Ministry spokesman Hamid Reza Asefi said British diplomats accepted that the men had strayed into Iranian territory.
Mr Adams said it was too early to draw similarities between his detention and the seizing of 15 British Navy personnel at gunpoint by Iranian forces on Friday.
The latest detention happened after British servicemen boarded a boat in the Gulf, off the coast of Iraq, which they suspected was smuggling cars.
"This is quite surprising actually," Mr Adams said.
"I don't know how similar this is to what happened to us. We were closer in shore. I'm quite concerned for the lads who have been captured.
"We were treated quite well, as well as could be expected. We got food and water, it was OK really."
He added: "It was very scary. At the time we didn't know what was going on, what was going to happen or even if we would be released.
"There was no dialogue until a translator turned up. They claimed they were holding us because we were in their waters."