The poem was a gesture of friendship by Lord Byron

Librarian Susan Stead stumbled across the original, which had been assumed lost, in an 1810 edition of The Pleasures of Memory by Samuel Rogers.

"I knew Byron and Rogers were acquainted so thought it probably was authentic," she said.

The poem's manuscript, which talks of friendship and memory, was dated 12 April, 1812.

It appeared in print four years later in a volume of collected poems.

Samuel Rogers was a patron of the arts and minor poet and The Pleasures was his most important work.

It was well received when it was published in 1792 and went through 15 editions before 1806.

Ms Stead said that it seemed likely Byron's poem was inspired by reading the book.

Literary salon

In 1793 Rogers set up a literary salon in London where he entertained writers, artists, politicians and actors.

He liked to present inscribed copies of his work to his friends and the copy held by the UCL is inscribed to "The Right Hon.ble The Lord Byron, from his obliged & faithful friend The Author".

Beneath this inscription is another in a different hand which says: "Afterwards returned by Lord Byron to Mr Rogers with the lines written on the other side."

Bryon's 12-line poem begins "Absent or present still to thee".

"I just opened the book and there it was," said Ms Stead who made the discovery during routine cataloguing.

She had the work authenticated by various Byron scholars.

Byron praised the Pleasures of Memory highly, in a letter to Thomas Moore in September 1813 he wrote: "His elegance is really wonderful - there is no such thing as a vulgar line in this book".

But he later turned against Rogers, writing a bitter lampoon against him in 1818.