A campaign to return the Elgin marbles to Greece is launched on Wednesday.
The Marbles were removed from Greece nearly 200 years ago
Run by umbrella organisation Marbles Reunited, it is based on research suggesting three out of every four British people want them returned.
The group wants them put alongside the other surviving Parthenon sculptures in a museum being specially built for the start of the Athens Olympics.
British ambassador to the Ottoman Empire, Lord Elgin, took them from the Greek capital's Parthenon in 1801.
The seventh Earl of Elgin, Thomas Bruce, then sold the marbles to the British Museum in 1816.
The British Government has repeatedly refused Greek Government requests to return them.
And the British Museum insists the marbles, which depict gods, men and monsters, are seen more in an international context in London than they would be in Athens.
Director Neil MacGregor said: "The British Museum is the best possible place for the Parthenon sculptures to be on display.
"The Parthenon marbles have been central to the museum's collections, and to its purpose, for almost 200 years," he added.
"The British Museum is a truly universal museum of humanity, accessible to five million visitors from around the world every year entirely free of entry charge.
"Only here can the worldwide significance of the sculptures be fully grasped."
But former British foreign secretary Robin Cook, actress Vanessa Redgrave and several
Olympic athletes support the campaign for the marbles' return.
Mr Cook has called the removal of the marbles a "dishonourable act of vandalism" but says the history of their move to Britain is not the key issue.
He told BBC Radio 4's Today programme: "The crucial question is that today Greece is not under the Ottoman Empire, it is not the war zone from which Lord Elgin was preserving the marbles - and let's assume he was right in doing it.
"The issue is where they should be now. There is really no dispute they belong in Athens."
The Parthenon marbles needed to be reunited and that could only happen by returning those in London to Greece, he argued.
Mr Cook suggested the British Museum could have an annex in Athens and in return would be able to show more Greek antiquities in Britain.
And the marbles would be well-protected in the new museum being built in Athens.
Asked why he had not backed their return when he was foreign secretary, Mr Cook said he had always held the same view but been unable to express them publicly when the government took a different line.
The current Lord Elgin said it was "completely untrue" to suggest his ancestor had plundered the Parthenon.
Instead, he had taken the marbles with the full authority of the Ottoman Empire, their then owners.
"It was a very carefully arranged expedition and the preservation and conservation was one of the finest things of its kind at the time," he said.
Athens might no longer be a war zone but atmospheric pollution had already caused serious damage to many of the marbles remaining there, he added.