The National Gallery is being urged to investigate the ownership of a painting believed to have been stolen from a Jewish family by the Nazis.

The Portrait of Amalie Zuckerkandl by Gustav Klimt is on loan to the gallery from the Belvedere Gallery in Vienna, as part of the exhibition, Facing the Modern: The Portrait in Vienna 1900.

But Randol Schoenberg, a lawyer who specialises in the restitution of significant artworks, insists the painting was looted.

Mr Schoenberg believes the work belongs to the family of the Jewish sugar baron Ferdinand Bloch-Bauer, who was a friend of Amalie’s and commissioned the work.

He said: “In 1928, Ferdinand Bloch-Bauer was forced to flee Austria and died in 1945. As explained in his will, his ‘entire property in Vienna had been confiscated and sold off’. His heirs never found the portrait.”

According to the Nazi inventory of Mr Bloch-Bauer’s house in 1939, the painting was still in his house nine months after he fled Austria.

It was later that “Amalie’s son-in-law came into possession of it during the war and sold it to the art dealer, Vita Kunstler,” said Mr Schoenberg.

Mrs Kunstler donated it to the Austrian gallery when she died in 2001 and, in 2006, an arbitration panel granted ownership to the Austrian state.

But Mr Schoenberg believes the arbitration panel made an error and that, under Austrian law, the painting should have been returned to Mr Bloch-Bauer’s heirs.

He urged that, before the National Gallery gives back the painting to the Belvedere Gallery, “it should request a new determination by the Austrian art restitution advisory board. That way, this misappropriated painting can finally be returned”.

The National Gallery said it had looked at the ownership of the work before it had borrowed it.

A spokesperson said: “The National Gallery has both legal and ethical obligations to ensure a work can be borrowed for an exhibition. There are also a number of international agreements with which we are obliged to comply.”

He added that the work was one of the paintings in the exhibition that had been given an immunity from seizure by the UK government.

As a result, the gallery had been “obliged to investigate the history of these paintings and publish its research on its website”, before taking it on loan.