There has been extensive debate since Monday about whether Israel's decision to raid the Gaza aid flotilla was legal. Douglas Guilfoyle, a maritime legal expert at the University College of London, says the raid itself could have been legal under international law - but only if the Gaza blockade itself is legitimate.

Al Jazeera: A lot of people are talking about whether or not Israel had any right to intercept [the ships].

Guilfoyle: Whether or not Israel had a right to intercept the ship on the high seas depends on whether it was engaged in a legal blockade. A blockade is a recognized tool of warfare that could allow the stopping and search of a ship on the high seas, but there are a number of requirements. There needs to be an armed conflict; the limits of the blockade need to be defined and properly publicized; and most importantly, a blockade should not proceed if it violates the principle of proportionality, if it inflicts excessive damage on the civilian population in relation to the concrete military advantage expected.

If those requirements were met, then yes, a ship could have been intercepted on the high seas, if there was a suspicion it was attempting to breach the blockade.

So who decides if a blockade is legal? If that's all it comes down to, it would appear to be an entirely subjective decision.

Well, each state is going to take its own view on whether or not it meets the requirements of international law. But I suppose a good metric is whether it's been accepted by other states, and there's certainly been a lot of condemnation of this blockade.

Where does that leave the international community, if it wants to pursue any kind of action against Israel?

The principle options would lie, I think, with the United Nations and with condemnation from the Security Council and action by other United Nations organs. I note that the Security Council has already called, this morning I believe, for a cessation of the blockade, referring to it as counterproductive and wrong.

It all depends to what extent Israel is prepared to cooperate, and we haven't seen a great deal of that when it comes to investigations in the past. But if another country wanted to launch an investigation... would it have any means by which to subpoena anybody in Israel, to force them to hand over what it considers to be crucial evidence or statements?

Well, it could certainly attempt to do so. That's going to turn on the national criminal law of the investigating state, or the investigating body. Compelling evidence from another state is difficult; it requires international cooperation, and may run into issues of state immunity or state secrecy when you're trying to get information out of a government.

If there's a United Nations investigation, in theory, the Security Council could call upon Israel to co-operate fully, and under the UN charter, Israel would be obligated to co-operate with that decision.

When it comes to establishing this blockade, a nation had to make announcements, it had to inform the international community that this was happening, that it was at war, etc. From what you've been able to learn, did any of that happen as far as Israel was concerned?

It's difficult, and I think something that commentators and international lawyers need to look at closely: whether there was proper notification of this blockade. It's been going on for a number of years, and normally if there had been notifications to what we call neutral powers, you'd expect [them] to show up in things like instructions to the merchant fleet in potentially affected flagged states. I haven't seen any of that; that doesn't mean it's not there, but it requires further investigation.

The real issue, to my mind, is the question of damage to the civilian population. If you have UN agencies saying insufficient aid is getting through to Gaza - and I've seen one BBC report saying what's getting through is less than one-quarter what they need on a daily basis - that alone, to my mind, raises serious concerns about the legality of the blockade, even if the formal requirements for notification have been complied with.

Where do you see this going now? Is there any point in anybody pursuing this legally, given the fact that, as many of us know, Israel has ignored countless UN resolutions over the course of the last 30-40 years?

That's a difficult question. I think... what speaking [about the] law does, in this situation, is it forms a channel through which political pressure is applied. And it certainly seems there's been an awful lot more pressure arising out of this incident in the international community, and it would seem within Israel itself.

So maybe this is an occasion we might see some kind of breakthrough, or at least a lessening of the blockade that is in place.

Source: Al Jazeera