Admiral Sir Alan West was First Sea Lord in 2004, when Iran detained eight British servicemen after they allegedly strayed over the maritime border.
Here he comments on the current detention by Iran of 15 Royal Navy personnel and compares it with the earlier incident.
How do the current events differ from 2004?
This seems to be something that has been orchestrated from Tehran. I think the incident in 2004, one can't be sure of it, but I think that was something that started locally and then Tehran became involved.
Why suddenly should an operation we do every day be aggressive and suspicious? It's absolute nonsense.
What was going on in the background in 2004?
That is more of a question for the Foreign Office but it was being resolved by diplomacy, through words with Tehran.
I have to say we saw that terrible treatment of our people then, which was absolutely outrageous. It would be outrageous if we were at war with a country - but we weren't actually at war with them. That was appalling and we did complain.
I don't know if maybe we were as robust as we might have been. They did release the people and that was the important thing, but we had huge trouble getting equipment back, which was effectively just stolen.
In fact, one of the boats was paraded and put into their military museum in Tehran as if this was some great victory.
The other thing about 2004 was that it was actually quite close to the Shatt al-Arab mouth, going up the river, where you can say, 'Well, it's quite close, where is the median line?', although they were clearly in Iraqi waters. This has taken place further out.
How can you tell which waters you are in?
It is highly complex. A commission is meant to meet to lay down the median line down the Shatt al-Arab and agree where the various lines are. So we have the line we believe is the correct one. We then make allowance the other side of it and make sure our craft operate well clear of that.
What kind of equipment would the navy have to guide them?
They have GPS and they have a system which allows communications. It means they know where the mother ship is and the mother ship knows where they are. GPS means they know their position exactly.
It's not like the old days when you went away in a boat and didn't really have a clue where you were. But all they had were small arms, they don't have heavy weapons. So of course to actually start fighting patrol boats would not be a clever thing.
What are the rules of engagement in this type of situation?
The rules are very much de-escalatory, because we don't want wars starting. The reason we are there is to be a force for good, to make the whole area safe, to look after the Iraqi big oil platforms and also to stop smuggling and terrorism there.
So we try to downplay things. Rather then roaring into action and sinking everything in sight we try to step back and that, of course, is why our chaps were effectively able to be captured and taken away.
If we find this is going to be a standard practice we need to think very carefully about what rules of engagement we want and how we operate. One can't allow as a standard practice nations to capture a nation's servicemen. That is clearly wrong.
How important are the British patrols?
I think they are very important. The Iraqi wealth depends on oil, the oil pipelines going through those big platforms. The terrorists did try to blow one up. They have managed to blow up lots of the other routes of oil going out of Iraq. So there's that importance. And, indeed, we are training up the Iraqi navy. It has been a huge success, and there is normally one Iraqi patrol vessel in the area. But it is also important to stop smuggling because smuggling is linked to terrorism.
What training would the personnel have been given to help them in the event of capture?
These particular people would not be trained in counter-interrogation techniques because they are not expected to be captured. But I think our guidance to anyone in that position would be to say what they want you to say, let's not be silly about it. Don't tell them secrets, clearly, but if they tell you: 'Say this', well if that's going to get you out, then do it. It means absolutely nothing, what they say, to be honest.