A previously undiscovered musical arrangement by Ludwig van Beethoven was performed for the first time at a British university on Thursday.

The two-minute long piece is an organ harmony to the 1,000-year old Gregorian hymn "Pange Lingua", University of Manchester Professor Barry Cooper told reporters of the discovery he made while studying a copy of a 192-year-old Beethoven sketchbook.

"Other scholars looked at it without realizing what it was as it looks like a random collection of chords. When I looked at it I saw the series of chords and saw a tune there," Cooper said.

"It's a Gregorian chant that I happen to know so I realized that he'd obviously harmonized the chant and produced a new composition."

The hymn had likely eluded other experts because the German composer had not included the words to the piece or the first line, which in a chant is usually sung unaccompanied, Cooper added.

"And Beethoven specialists tend not to be specialists in plainsong hymns and specialists in Gregorian chant don't normally look at Beethoven sketches," he said.

It is thought the hymn was penned for the composer's friend Archduke Rudolph of Austria, for whom Beethoven also wrote the "Missa Solemnis", or Mass in D, when the archduke was made an archbishop around 1820.

"The dates match up nicely: he transposed this Gregorian chant into an unusual key that fits well with his mass in D. It seems more than a coincidence," Cooper said.

Cooper, a leading Beethoven expert, enlisted the help of a group of music students to put on the first known performance of the composition at Manchester University in northern England on Thursday afternoon.

The short hymn is significant because it marks a rare experiment into religious music for Beethoven, who died aged 57 in 1827.

"He wrote only two masses and didn't write any simple, functional liturgical music like what we have here. It's the first piece in this genre in his hand," Cooper said.

"It doesn't turn the knowledge we have about him upside down but adds a little and that is always interesting.