History catches up with thieves of opportunity

In the interview, Williams said the British Museum wanted to "change the temperature of the debate" around the Marbles.

He added that all sides need to "find a way forward around cultural exchange of a level, intensity and dynamism which has not been conceived hitherto".

According to a survey by YouGov, a research and data analytics company in the UK, public opinion in Britain is increasing in favor of returning the Marbles with 59 percent of respondents saying that the Marbles belong to Greece in a recent poll, compared to 37 percent in 2014.

Charlotte Woodhead, an assistant professor at Warwick University's School of Law, previously told China Daily that some national museums in Britain are prevented from returning objects due to specific statutory governance, "even where they consider themselves under a moral obligation to do so".

"This was tested in a legal case in 2002, and while this prohibition on transfer has been lifted in the case of certain human remains and Nazilooted cultural objects, it remains for many other objects in national museums," Woodhead explained.

The fate of many objects is also subject to existing conventions.

"Where an object has been wrongfully taken and has been in England or Wales since before the 1980s, a legal claim in court is unlikely to succeed because, usually, the effect of the statute of limitation would be to extinguish the original owner's legal title to the object after six years," Woodhead said.

She said items that arrived in England or Wales after 1981 also would not likely be the subject of a successful claim from the original owner if they were bought in good faith.

But she added that museums are obliged under the UK Museums Association Code of Ethics of 2015 not to acquire items that were "wrongfully taken during a time of conflict" and also to deal "sensitively and promptly with requests for repatriation".