German composer Ludwig van Beethoven is believed to have written the rediscovered organ arrangement for a Gregorian chant. (Associated Press)

A previously unknown Beethoven arrangement for an ancient hymn was performed in Manchester on Thursday after being lost for more than 190 years.

University of Manchester professor Barry Cooper found the work in a sketchbook dating from about 1820 and held at the Berlin State Library.

He said it appeared the arrangement is an organ harmony for the Pange Lingua, a 1,000-year-old Gregorian chant.

Other experts in Ludwig van Beethoven’s work may have overlooked it because it looks like a random assortment of chords, rather than a complete piece. It only makes sense as an arrangement if put together with the chant, a form of music not associated with the great composer, Cooper said.

“This is quite an exciting discovery to find a piece like this which we didn’t know Beethoven had written. It’s quite rare,” Cooper told the BBC.

“I’m amazed no one’s looked at it before. I’m also amazed Beethoven would write a piece like this because there’s nothing in his other known output that’s anything like this piece.”

Cooper is the same Beethoven expert who stirred controversy in the classical music world by creating a 10th Symphony based on unfinished Beethoven sketches.

The two-minute hymn was being performed by students at the University of Manchester on Thursday afternoon.

Experts in Berlin had assumed the piece was a sketch for Missa Solemnis, a mass Beethoven created around the same time and one of his very few pieces of liturgical music. Few experts associate Beethoven with ordinary church music, Cooper said.

The arrangement may have been played on the organ in March 1820, when Beethoven's patron Archduke Rudolph of Austria was made Archbishop of Olmutz, he said.