From the Benin bronzes to the Parthenon marbles, debates over the restitution of cultural artefacts are now a fact of life in an international art world forced to reckon with the often controversial history of its treasures.

Museums around the world are having to consider implications of retaining items many argue were taken from their owners under persecution or duress.

But while many of the rows over restitution pertain to centuries-old pieces, the recovery of which is complicated by the sweeping periods of time that have passed since their removal, a new documentary shows how the fight to recover more modern artwork can be just as problematic.

The Spoils follows the continuing attempts to restitute the assets of a German-Jewish art dealer, drawing attention to how loaded a political and cultural issue restitution has become.

The film, which premieres in the UK as part of the Jewish film festival, follows two fraught restitution cases and two botched exhibitions attempting to honour Max Stern, who liquidated his Düsseldorf gallery in a Nazi-forced auction in 1937.

“The issues in the film go beyond the Holocaust and resonate with larger questions facing the art world right now,” the film’s director, Jamie Kastner, said.

“In recent years restitution has become an endlessly loaded political and cultural issue – be it over antiquities, colonial plunder, the Benin bronzes, the Parthenon marbles, or last week a Monet from Austria.

“Across all the disputes, there’s a familiar pattern: politicians and museum officials, having ignored the claim as long as possible, finally start making noises about ‘doing the right thing’. But inevitably, things get gummed up in endless legal, scholarly or ‘scientific’ wranglings that drag on and on.”

Max Stern owned the popular Galerie Stern in Düsseldorf in the 1930s, but was forced out of business by the Nazis. He had to sell all his paintings at auction for rock-bottom prices, while his accounts and assets were frozen and seized.

He fled Germany for the UK, where he was interned for two years before being sent to Canada. In Montreal, he established himself as one of Canada’s greatest art dealers, representing the likes of Rodin, Henry Moore and discovering Emily Carr.

Stern died childless in 1987 and bequeathed the bulk of his estate to McGill and Concordia universities in Montreal, and the Hebrew University in Jerusalem. In 2002, his estate launched an initiative to recover his lost art.

So far, the Max Stern Art Restitution Project has restituted 25 paintings, making it the most successful project of its kind in the world. But hundreds of Stern claims are still pending.

“This isn’t just another historical story, it’s a brawl that is going on right now around an issue which most people would imagine was settled long ago,” Kastner said.

“I couldn’t believe that people were still at each other’s throats over world war two art. There was an alarming tone-deafness to these minute hagglings, in contrast to the enormity of the Holocaust.”

The film focuses on the project’s successful attempts to restitute two paintings: Wilhelm von Schadow’s self-portrait and The Artist’s Children from the City of Düsseldorf in 2014 and 2023, respectively.

The process was extremely fraught, with lawyers and even the former mayor of the city becoming involved. Under the allied restitution principles, now accepted as general rules for restitution cases, the person or estate making a claim has to prove that their assets changed hands under persecution or duress.

“It then becomes a legalistic wrangling over the fine points of what constitutes duress and when duress actually began in Germany for Jews,” Kastner said. “So they’re arguing about things like, ‘how much were Jews like Stern suffering in the spring of ’33 versus the fall of ’35? Does this or that constitute persecution?’”

The issue has arrived in the UK too. Stern’s heirs are now seeking to restitute a painting in the collection of the Tate – Jan Griffier the Elder’s View of Hampton Court Palace, which was bought by the gallery in 1961.

Though the painting was the subject of a previous restitution claim in 1999 (after which the British government paid compensation to the heirs of a Jewish banker), the Stern project say they have serious concerns that compensation was paid to the wrong heirs. They say newly uncovered documents show the painting was in the Stern collection at the time he was forced to sell his assets.

They also believe that another of Stern’s paintings held by the National Trust, Joachim Patinir’s The Temptation of Christ, which is part of a collection at Upton House, is also eligible for restitution as it was sold by Stern under Nazi persecution.

Kastner, whose previous documentaries include There Are No Fakes – credited by police with inspiring the investigation that cracked the world’s largest art fraud – said the lesson from his film was that “nothing ever happens or is achieved easily”.

He added: “In this story, the battle lines were not obviously drawn. It wasn’t exclusively Germans versus Jews. There are always people on both sides of the debate deeply committed to doing the right thing.”