Richard Westwood-Brookes, who is selling the items, said: “This just sounds too good to be true, but the vendor’s father spent a lifetime proving it.

“He compiled a 300 page document and spent a great deal of money engaging experts to examine the etching.

“The signatures in pencil on the reverse are said to have an 80 per cent chance of being genuine, and there is proof that Emma Lowenstramm did exist.

“The circumstantial evidence is very good on top of the paper having been tested.”