Sotheby's in Milan was caught shipping a painting to London to get a better sale

According to the United Nations, Italy holds more than half of the world's cultural treasures - but thousands of these are being smuggled out every year.

The increased number of cases of illegal export is being blamed on a combination of widespread excavation, fraud, questionable practices by some auction houses and laws that some see as highly restrictive.

"Nobody takes the law really seriously," Michel van Rijn, a former smuggler who now advises on suspicious art dealing, told BBC World Service's Assignment programme.

"There's a non-stop supply of artefacts leaving the country on a daily basis."

impossible task

According to Unesco, the UN's cultural body, Italy has more precious and historic art than the rest of the world put together.

But this means it is subject to more criminal activity.

"It's an impossible task to police it all," argued Daniel Berger, a former American museum official now working in Italy.

"Not even a police state could do that, and Italy's the opposite of a police state."

This kind of crime is an offence against humanity Italian arts minister Rafaeli Squitieri

The Italian police database on stolen art - named Leonardo - has been somewhat successful in helping police recover artwork that has been taken from various museums, churches and private collections.

And the head of division charged with keeping art in the country - the Cultural Patrimony Division - has said he is "very satisfied" with the results.

The police say the number of major art thefts recording in Italy has fallen by nearly half in the last two years - but this does not give the whole picture, as there have only been a handful of successful prosecutions.

And it has not helped tackle many other aspects of the Italian art crime wave.

One area of concern is the number of ancient pots, coins and relics on sale at many markets in the country's principle cities - illegally excavated from Italy's hillsides.

"The local people consider the things that they find in the ground as being left by their ancestors for them," Mr van Rijn explained.

"They don't see the law in that sense, because it's just a gift from their ancestors."

Difficult situation

Items older that 50 years are subject to highly restrictive laws governing whether they can be taken out of the country.

This places Italy's auction houses in a difficult situation. Since Italy has much more art than anywhere else, the prices they receive are likely to be much lower than in New York or London.

They therefore have an obvious conflict of interest - staying within the law, while trying to get the best price for their artwork.

Davide Sestieri, the director of Rome auction house Finarte, said that a painting by Carlo Dolce had sold in New York for nearly double the price an equivalent piece had sold in Italy.

In 1997, the Milan office of the world's largest auction company, Sotheby's, was caught shipping an unlicensed painting to London, in order to achieve a better sale.

In Florence, Assignment spoke to a dealer at one auction house, Pandolfini, who recommended that if a foreigner wants a piece of art, they get someone Italian sign for a sale.

"He buys it, we make an invoice, and there are no complications at all," said Claudia Canjoli.

Exporting freely

Pandolphini responded by saying Ms Canjoli's comments were made "conversationally" and it "would never advise its clients to act illegally".

Italian police say major art theft has nearly halved in two years

But Mr van Rijn said that it was not just Italy's auction houses who were behind the "non-stop supply of Old Masters" leaving Italy.

Private collections by wealthy families are also being rapidly sold off. Although some are registered with the authorities, many are not - and even if they are, there is a way round it.

"You have so many old families who have things in their collection which are not notified with the department of cultural heritage, so they can export freely," he said.

"If they have been notified, you just have a copy made, and have the copy on the wall. If the inspector comes and says 'it's a forgery,' you say 'oh my God, did I inherit a forgery? What a shame'. There's no way to control all this."

Italy's Arts Minister Rafaeli Squitieri promised that laws - for every kind of cultural crime - would be made tougher.

"I'm very unhappy that these criminals are not always captured and sentenced," he told Assignment.

"Our Italian law is not very rigorous. Soon we will present new laws to prosecute these people.