One of Britain's leading art galleries faces the threat of legal action over three paintings by the 17th-century Flemish master Peter Paul Rubens from the granddaughter of the works' former owner who was murdered by the Nazis.
Christine Koenigs, who lives in Amsterdam, told The Independent on Sunday that she would press ahead with her claim against the Courtauld Institute of Art in London, despite a finding this week by the Government's Spoliation Advisory Panel that the paintings were lost for economic reasons.
Ms Koenigs is a member of one of two Dutch families who are taking legal action to reclaim art collections lost during the Second World War. However, rather than reclaiming masterpieces that were looted, the claimants in these cases argue that the paintings were sold under duress.
The Katz family in the Netherlands is seeking the return of 227 works, including pieces by Rembrandt and Jan Steen, which currently hang in some of the region's premier galleries and museums. Their claim is being considered by the Dutch government.
In America, a claim was lodged in court last month against Leonard Lauder, the billionaire scion of the Lauder cosmetics fortune, for the return of a Gustav Klimt painting, Blooming Meadows, which he bought for 4m in 1983. Georges Jorisch, of Montreal, claims it was stolen from his grandmother by the Nazis.
Ms Koenigs has spent more than a decade fighting for the return of her grandfather's extensive art collection which includes among its hundreds of works, not only the three Rubens now owned by the Courtauld but also the Portrait of Dr Gachet by Van Gogh. The current owner of this painting is unknown, but it broke records when it was sold at auction in 1990 for $82.5m (41.2m).
The disputed works in the Courtauld Institute are St Gregory the Great with St Maurus and Papianus and St Domitilla with Ss Nereus and Achilleus, The Conversion of St Paul and The Bounty of James I Triumphing Over Avarice.
Ms Koenigs's grandfather, Franz, was a wealthy German banker who lived in the Netherlands. He had used his collection, part of which was on display at the Museum Boymans in Rotterdam, to secure a bank loan in 1931. The Courtauld said that he lost the right to the works when the bank went into liquidation days before the Nazi invasion on 10 May 1940, arguing that it was an economic decision and not a result of war.
Eventually, amid a series of deals under the shadow of the Nazi invasion, the works were sold to Count Antoine Seilern. The collector, who had British nationality, is said to have collected the paintings in 1945 while still in his British army uniform, piled them into a Jeep and taken them out of the country without an export licence.
When he died in 1978 he bequeathed his by then extensive collection, known as the Princes Gate collection, to the Courtauld. Worth $50m at the time, it was one of the biggest bequests ever.
But Ms Koenigs argues that the Jewish bank went into liquidation purely to protect its assets until after the war and the plan had been to take the Koenigs' collection out of Europe to keep it out of the hands of the Nazis. Moreover, she says, her grandfather was not asked to repay the loan before it was foreclosed, and was on friendly terms with the bank's owners. It was always his intention to reclaim the works after the war, but, says Ms Koenigs, as an opponent of Hitler who had been feeding information to the Allies, he was pushed under a train in Cologne in 1941.
Ultimately the plan to keep most of the art from the Nazis failed. Some works were seized by Goering, who collected looted works for Hitler. Hitler bought a substantial part of the collection in December 1940.
"I will approach the Secretary of State and if the reply is not satisfactory then I will be taking legal action," Ms Koenigs said. "The panel's report is flawed and relies on a judgment of the Dutch government that the bank foreclosed for economic reasons. They have taken the whole thing out of context of the war. We seek restitution to reunite the paintings with the life achievement of my grandfather."
A Courtauld spokeswoman said: "The Courtauld Institute of Art appreciates the thoroughness of the Spoliation Advisory Panel's examination of this case and is pleased that its findings confirm that the three works rightfully form part of the collection of the Samuel Courtauld Trust, displayed for the public benefit at the Courtauld Gallery."
'The Conversion of St Paul' c1610-12, by Peter Paul Rubens. One of the three disputed oil sketches at the Courtauld Institute. A panel that dismissed a restitution claim last week ruled that the pictures were not stolen by the Nazis.
'The Bounty of James I Triumphing Over Avarice', c1632. Oil on panel. Rubens. The sketches were in private hands for 40 years before the bequest to the Courtauld. A Rubens sketch was sold by Christie's last week for 3.8m
'Saints Gregory, Maurus, Paianus and Domitilla', by Rubens, 1606. The third disputed Rubens belonging to the Courtauld Institute. All three were bequeathed in 1978 when collector Count Seilern died.
'Michale Ophovius', 1618, by Rubens. Another Rubens claimed by Christine Koenigs, whose grand-father built up an extensive collection of the artist's work. This portrait is thought to be kept in a Madrid bank vault.
'The Quarry of Bibemus' by Paul Czanne, c1898. One of a series of works on this subject. This one is at the Folkwang Museum, Essen in Germany. It formed part of the Koenigs' collection but is not being actively pursued at the moment.
Sold in 1990 for 41.2m
'Portrait of Dr Gachet' by Van Gogh, 1890. Painted in the last few years of the artist's life and another from the original Koenigs collection. It was sold at auction in 1990 for a then record 41.2m. Current location unknown.