However, the private collector who owns the untitled work has said he will not press charges against the unnamed 40-year-old attacker.

The piece was on display as part of the Museum of Salo’s “Museum of Madness” exhibition, and museum president Giordano Bruno Guerri said the attack fit with the theme of the show.

Mr Guerri said: “The show about madness would not have been complete if it did not host an episode of madness.”

However, the exhibition’s curator, Vittorio Sgarbi, said even critics of Hitler should not reproduce “the censorship and hatred expressed by dictators” by attacking unpleasant pieces of art.

The painting in question, he added, is “a piece of crap”.