The discovery of an art forgery scandal to rival the infamous Knoedler ring of fake masterpieces is sending shockwaves through the art world.

In what is being described as “the biggest art scandal in a century” collectors are understood to have paid as much as £200 million for fake paintings believing them to be genuine masterpieces. According to a French investigation, up to 25 forgeries of Old Masters may be in circulation including copies of works by Lucas Cranach the Elder, Frans Hals, Orazio Gentileschi and others.

Most of the pieces are alleged to have derived from the collection of André Borie, a French civil engineer. When Borié died in 1971 his daughter Andrée inherited the collection and subsequently gifted and sold several of the paintings to French dealer Giulano Ruffini with whom she had an eight-year affair. Ruffini denies having presented the works for sale as genuine Old Masters. “I am a collector, not an expert”, he has stated.

Suspicions over the authenticity of the disputed works were first raised in March this year when Cranach’s ‘Venus with a Veil’ (1531) was seized by French authorities while on exhibit in Aix. Linked to the Cranach is a ‘Portrait of a Man’ purportedly by Hals and bought by London dealer Mark Weiss. Weiss sold it to a US collector in a ‘private treaty’ sale brokered by Sotheby’s but when the collector learned of the Cranach’s fate he complained to the auction house. Sotheby’s was forced to reimburse him and are said to be threatening Weiss with legal action.

Other works forming the subject of the French investigation include a portrait of Cardinal Borgia after Velázquez and ‘David Contemplating the Head of Goliath’ attributed to Gentileschi and recently on loan to the National Gallery in London.

Art dealers involved in the sale of the suspected works have insisted they had no reason to doubt their authenticity. In response to news of the Cranach’s seizure, Konrad Bernheimer of London’s Colnaghi Gallery who bought the ‘Venus’ in 2013 told reporters that he was “totally confident” in the attribution.

The difficulty in detecting the fakes stemmed from the meticulousness of the forger. Quite unlike the artist implicated in the Knoedler trials who was once careless enough to misspell Jackson Pollock’s name, the forger in this scandal was described by one dealer as “the Moriarty of fakers”.

Nonetheless, art dealer Bob Haboldt told the Daily Mail that those who fell prey to the forgery ring ignored vital warning signs that something was amiss about the works. “They lack any credible provenance and references in the numerous publications about these artists. The latter should have made the principal dealers suspicious”, he said.