The British Museum tells us that the Elgin Marbles are looked after better in London than they would be in Athens. The number of incidents involving artefacts disappearing from the museum might suggest otherwise however.
BBC News 
Last Updated: Monday, 1 November, 2004, 15:17 GMT
Chinese jewels stolen from museum
Items of rare medieval Chinese jewellery have been stolen from the British Museum in London.
The 15 pieces were stolen by a thief believed to be masquerading as a visitor to the museum on Friday.
“We believe the theft took place while the gallery was open to the public as no alarms were activated and there was no sign of a break-in,” said police.
The theft of the “historically important” items was not discovered by staff until Saturday morning.
Police will investigate the possibility that the Chinese jewels, including ornate hairpins and fingernail guards, were stolen to order for a private collector.
Despite a sophisticated security system and guards patrolling the museum, there have been two major thefts from the British Museum since 1990.
In 1990, a 17th-Century Japanese statuette worth £100,000 vanished from the museum in central London, home to the Rosetta Stone and the Elgin Marbles.
In 1993, burglars broke in through the roof and stole £250,000 worth of Roman coins and jewellery.
The Independent suggests that the theft may have been carried out by the same people who have carried out previous raids on the V&A
The Independent 
Theft of medieval Chinese jewels from British Museum follows raid on V&A
By Louise Jury, Arts Correspondent
02 November 2004
Police investigating the mysterious theft of medieval Chinese jewellery and ornaments from the British Museum late last week believe the raid could be linked to the theft of Chinese jade from another London gallery last month.
About 15 small decorative items, including hairpins, nail guards and jewellery, were taken from the British Museum’s oriental antiquities gallery between 10am on Friday and 10am on Saturday. A police spokesman said no glass cases had been smashed, no alarms were triggered and there was no sign of forced entry. “We believe the theft took place while the gallery was open to members of the public,” he added.
The museum refused to put a value on the items but called them as “historically important pieces” dating from between the 12th and 16th centuries.
Four weeks ago, the Victoria & Albert Museum lost nine jade cups and bowls worth £60,000. In the well-organised theft, on the afternoon of 4 October, thieves used instruments to break into a cabinet in its ceramic galleries. Three small cups and a bowl, two small ornamental plaques, one small ritual cylinder and two small animal figures, all made of dark, green-brown jade, were stolen. Most dated from between the 15th and 19th centuries but the cylinder was dated earlier than 1,000BC.
A V&A spokeswoman said: “There may be similarities to the theft at the V&A last month and we are speaking to colleagues at the British Museum.”
There has been growing interest in oriental items, particularly among the emerging nouveau riche in China and wealthy residents in Hong Kong keen on reclaiming parts of their cultural heritage.
All the major auction houses in London have major Asian sales next week. Among them is the auction at Christie’s of a dazzling collection of items which belonged to the 19th-century millionaire merchant banker Alfred Morrison, at Fonthill House, Wiltshire.
Many were purchased directly from Lord Loch of Drylaw who had brought them to Britain after the Imperial Garden in Beijing was attacked. It was burnt by British and French troops in 1860, partly restored then sacked and burnt again in 1900 by troops from Britain, the United States, Germany, France, Russia, Japan, Italy and Austria.
Alexandra Smith, operations director of the Art Loss Register, said it seemed likely the thefts at the British Museum and the V&A were linked, but it was also possible that the second one was a copycat attack.
“That happened in country houses where there was a spate of them,” she said. But it was difficult to know whether it was a gang or simply opportunists.
“Just because people are stealing from museums doesn’t mean it is a big, organised thing. But it is amazing that someone had the guts to do that from the British Museum.”
The demand for Chinese items seemed evident from the auctions just held in New York and Hong Kong and now in London, Ms Smith added. “If there are big sales, it does tend to mean there’s a demand.”