Late last year the MV York, which was heading to the Seychelles, was hijacked, and now it is being used as a base for pirates who can use it to stay at sea for months and carry their lightweight attack craft.

Experts warn that this is just one of five similar vessels - some of which, like the MV York, are carrying cargos of gas or oil which make them almost impossible for foreign forces to attack them.

So far this year at least 20 ships have been attacked and about six captured - their crews being held in appalling conditions off the coastal towns of Hobyo and Haradheere.

According to Oceans Beyond Piracy, a study group of experts from 18 countries, the cost of extra insurance for crossing through waters affected by pirates in Somalia is close to £2bn a year.

Ransoms for ships and their crews have skyrocketed - the average "fee" in 2005 was £100,000 while in 2010 it climbed to £3.3m.

And the average length of time hostages spend in captivity while lawyers and agents working for insurance companies haggle over the price of their release is close to eight months.

The International Maritime Bureau's most recent survey shows that there were 1,181 hostages taken last year, with around 700 still being held on about 30 ships.

"These are the highest figures we have ever seen," said captain Pottengal Mukundan, director of the International Martine Bureau's Piracy Reporting Centre.

Even though the combination of naval task forces have caused a drop in attacks in the Red Sea and the Gulf of Aden, they have been unable to prevent the long range pirates in the larger "mother ships".

"These vessels are as fast as most commercial shipping, they offer a stable platform to fire on a bridge from, and they can spend months at sea," said Gary Porter, head of security for the Danish shipping company Clipper Group.

"The use of these ships is a very dangerous situation - they have a perfect firing platform and they're going to cause extensive damage."

So, some ask, why do the Somali pirates get away with it? Why can't they be shot, sunk or arrested when they attack - and jailed when they're caught?

The answer lies in complex maritime law.

Stephen Askins, a a lawyer with Ince in London, explained that Nato and the EU do not "have a mandate to make war against Somali pirates" which means that pre-emptive attacks are forbidden.

"There are at least 29 ships and 700 hostages being held off the coast of Somalia - a rescue attempt would be tough enough on one ship but that many is impossible.

"And while some companies are looking at putting armed guards on their ships they will be governed by the laws of the nation whose flag they are flying.

"There is a right of self-defence, but who decides when and how to use lethal force?"

The result - according to a consortium of experts from 18 nations - is "a critical tipping point" which could permanently shift "maritime trade patterns".