The poet Siegfried Sassoon was on convalescent leave from the Western Front when, out walking one day, he was overwhelmed by a ''paroxysm of frustration'' and hurled his Military Cross into the Mersey. It was a passionate gesture that expressed all the rage and pain welling up inside one of the nation’s greatest war poets after his experiences in the trenches.

Or so it was widely thought, until the long-lost gallantry award turned up in a chest in his son’s attic in the Isle of Mull last summer.

The officer known as ''Mad Jack'' for his near-suicidal feats of daring had instead thrown the dress ribbon into the river. The medal itself will now be auctioned at Christie’s in London on June 6, where it is expected to fetch up to £25,000, about 200 times the value of an average First World War Military Cross (MC).

Thomas Venning, director of the book and mansucript department at Christie’s,...[said,]
''Around the time that he threw the ribbon into the Mersey, Robert Graves was helping to persuade Sassoon’s colonel not to court-martial him. The Army sent him to Craiglockhart Hospital to be treated for shellshock, where he met Wilfred Owen.'' [The award-winning Regeneration trilogy by novelist Pat Barker is based on Sassoon, Owen, and the military psychiatrist W.H.R. Rivers.]...

[The poet died in 1967. A stepson of Sassoon's only child,] who is selling the medal on behalf of the family, said yesterday: ''I had no idea it even existed. Like most people, I thought it had been thrown into the Mersey.

''I found it while clearing out the attic of the family property on Mull. Bizarrely, it was in a treasure chest, like a pirates’ chest, covered in cobwebs and long-dead insects. The ID tag was there too, along with the revolver in an old Jiffy bag and some poetry medals.''