Shattered museum displays do not have the heart-thudding impact of bombs and bodies, but among the most memorable images after the fall of Baghdad last year were the chaotic scenes of looting in the city’s museum.

One of the museum’s most prized possessions, the 5,200-year-old Warka vase, was stolen, and the Harp of Ur was broken and stripped of its gold. Donald Rumsfeld, the American Secretary of State for Defence, said of the pillaging: “Stuff happens.”

Eighteen months later, the museum has recovered many of its treasures. An amnesty was offered on stolen items and three men brought the Warka vase back in June in the back of their car.

The real scandal now is not theft from institutions, which are under 24-hour guard, but the plundering of Iraq’s most ancient archaeological sites. Freelance excavators are hunting not for grand artefacts, but instead seals, inscriptions and earthenware — Iraqi treasures which still lie, undiscovered, in the earth.

The country’s oldest cities — Isin, Uruk and Nineveh — are being robbed. Unlike the Baghdad museum, there are no inventories to say what untold treasures have been lost.

“The problem with Iraq is if you dig pretty much anywhere, you’ll find something ancient and interesting,” an officer in Interpol’s Stolen Works of Art Department says. He estimates that looted antiquities worth millions of pounds are being spirited out of Iraq for private collections.

Donny George, the director- general of the Iraq Museum in Baghdad, says: “The looters turn up and start digging every day. Nobody can expect one guard to fight off 300 looters armed with machineguns and rocket launchers. I know the security forces have other priorities, but this isn’t just about Iraq. This is about how it all began. After all, human civilisation started in Mesopotamia.” It was in these lands between the Tigris and Euphrates rivers, thousands of years ago, that human beings started to farm, write, make laws and build. Ever since the 19th century, archaeologists have swarmed over Iraq.

Sarah Collins, a curator with the Ancient Near East Department of the British Museum, worked with the Baghdad museum for several months last year during the amnesty for looters. “People were bringing things back, but we were also getting things which had clearly just been taken from the ground. You just couldn’t tell where from. Quite often they wanted money. We couldn’t buy them. It would just encourage them to dig up more. Looting wasn’t a problem under Saddam. He beheaded a couple of looters and that put a stop to it.”

It is still a vicious business. The bodies of eight Iraqi customs officers were found earlier this month, south of Baghdad. The men had been kidnapped as they were taking a cache of Sumerian artefacts to the museum.

Iraqis working for foreigners are approached by touts, asking if their expatriate clients would like to buy, for a couple of hundred dollars, a 3,000-year-old Sumerian cylinder seal that would sell normally for £10,000.

According to Mufid al-Jazairi, the Minister of Culture in the Iraqi interim Government, there is a network of middlemen who come to the villages, then sell on to the major dealers.

There are efforts to curb the looting. A plainclothes policeman, who read archaeology at university, oversees an anti-looting department and tries in desperation to buy back artefacts himself.

Last year, a retrospective law was passed in Britain making it illegal to own Iraqi artefacts brought out of Iraq after 1991. An art dealer in America was imprisoned earlier this year for possessing Iraqi antiquities. Interpol has arranged two international conferences on the problem.

“Unfortunately, a lot of the items, like cylinder seals, are very small,” Sarah Collins says, “and customs officers are looking for weapons, terrorists and guns.”

Interpol admits that pieces vanish into Switzerland, then come out with certificates asserting that they were dug up in Syria or Turkey.

The hunt is not fruitless. Smugglers are arrested. Al-Jazairi estimates that 2,000 artefacts are sitting in warehouses in Jordan, Syria or other neighbouring countries, waiting to be returned to Iraq.

“Unfortunately, it is a question of proof,” Collins says. “Someone has to prove legally that it came from Iraq. That’s hard — an expert can say where and when it was made, but we can’t prove where and when it was dug up.”