As in the latest case, the decision often rests with an artist’s descendants, who are indefinitely allowed to exercise the “moral rights” of their forebears under French law. Similar committees decide whether works apparently by Edgar Degas, Pablo Picasso and Man Ray are genuine. Yet, as Valentin puts it, “The children, grand-children or great-grandchildren of an artist are not necessarily the best experts.”

Mould argues that the system ought to be reformed. “The son of a brain surgeon is not someone you would trust to work on your brain,” he says. “After all, they hold a very powerful right: they can turn something bought for £5 in a flea market to £1 million. Conversely, as in Martin’s case, they can turn £100,000 to nothing.”