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Already, though, a debate has started as to what its legal status may be, with opinion veering between Nazi loot and the legitimate property of the man in whose apartment it was found.

The revelation that 1406 drawings, prints, watercolours and oils with a provisional valuation of close to €1bn now reside in a suburban customs warehouse promises to provoke a flood of restitution claims.

The trail began in September 2010 when a cross-border customs sweep of a train from Switzerland to German found 80-year-old Cornelius Gurlitt carrying large quantities of cash. When tax authorities went to his unassuming flat in the Schwabing neighbourhood of Munich they discovered pictures by artists including Kirchner, Chagall, Matisse, Picasso, Toulouse-Lautrec, Courbet and Canaletto behind shelves of decades-old foodstuffs.

Mr Gurlitt is the son of Hildebrand Gurlitt, an art dealer and former director of the museum in Zwickau (he left the post in 1933 because he was half Jewish) who was given the task of selling 'degenerate art' from German museums for hard currency abroad. He also bought many works from private owners until the end of the war.

Sale of Works

It seems that his son survived for the next 60 years by selling off some of the works as a means of support. Only weeks prior to the seizure of the collection, Cologne auction house Lempertz had sold Lion Tamer, Circus, a gouache by Max Beckmann (a picture once owned by the Jewish art dealer and collector Alfred Flechtheim, but not one on the Art Loss Register's list of Nazi-looted work) for €864,000.

Gurlitt, who had no declared income but more than €500,000 in bank accounts, has been charged with tax evasion and money-laundering.

The issue of ownership promises to be extremely complex. While at least 200 pieces are thought to be on lists of pictures missing since the Second World War (a portrait of a lady by Matisse once belonged to the dealer Paul Rosenburg), others may have been acquired legitimately by Hildebrand Gurlitt. At least some of Gurlitt's pictures were confiscated by the Allies after World War Two, but later returned to him.

Thus far only snapshots of the contents of the flat have been published and Jewish groups are among those that have called for more information to be made public immediately.