German art historian Meike Hoffmann has been trying to establish the origin and value of around 1,500 artworks found in Munich that were looted by the Nazis in the 1930's and 1940's.
One of the works was reported to be a Matisse painting previously owned by Jewish collector Paul Rosenberg.
His granddaughter Anne Sinclair, the French journalist and ex-wife of the former head of the International Monetary Fund Dominique Strauss Kahn has been campaigning for many years for the return of looted art.
More top news
Hot and humid throughout the Bank Holiday Weekend.
The airline has cancelled all flights from Heathrow and Gatwick before 6pm on Saturday.
The Hollywood couple, who have been married for 17 years, said they still have "tremendous love and respect for each other".