£300m of artworks lost to UK since 2011
Almost £300m of the UK's most cherished artworks have permanently left the country over the last five years.
They include a marble statue of Aphrodite, the Greek goddess of love and beauty, valued at £9.6m, which a dealer wanted to export to the Republic.
The sculpture had stood in Syon House, the London home of the Duke of Northumberland.
Stephen Deuchar, director of the Art Fund, said the export system was abused by wealthy buyers using "exploitable loopholes" and "gentlemen's agreements" to keep masterpieces out of public reach.
Also among the exodus of treasures since 2011 was a £50m Picasso - Child With A Dove - now thought to be in Qatar.
Important cultural objects bought by overseas collectors are typically issued with a temporary export ban, giving British dealers or museums a chance to match the price.
Some 32 "national treasures", worth a total of about £70m, have stayed in the UK this way since 2011-12, Arts Council figures show.
Recently, a New York-based buyer refused to sell a £30m Pontormo painting to the National Gallery despite the institution raising the asking price.
Dr Deuchar said this happens "time and again", adding: "Applying for an export licence, you have to promise if a museum raises a matching sum you will sell it to them.
"We (the Art Fund) want to see some proper legal muscle to a system currently based on gentlemen's agreements... the civil servants running it need to listen to people who have new ideas for change."
But leading art historian and dealer Bendor Grosvenor argued that Britain's export system was "probably the best in the world" as it balanced the rights of the public and private collectors.
He said: "Art is a global business... is it in the public interest for the State to effectively seize someone's private assets? Something about art brings out the socialist in everyone."
Mr Grosvenor added: "We sometimes think it must belong to the people."