Sotheby's Dr Steven Roe: "It's a lovely piece of music"

The autographed manuscript of the work - valued at between £150,000 and £200,000 - will be put up for sale at the auction house in December.

The composition, which was found in Cornwall, has never been published before and is said to be in the German composer's own hand.

Dr Stephen Roe, head of Sotheby's Books and Manuscripts, said the recital was an historic occasion.

Members of Eroica give the music its first public airing

"This piece is probably receiving its first performance ever here. We can't be sure it wasn't performed in Cornwall by the Smugglers Cove string quartet but I would have thought it was unlikely."

"When I saw it, I knew it was Beethoven's hand but I couldn't put it in the context of Beethoven's work, because there were no quartets in B minor," he said.

"The true moment of discovery was today, when I heard it for the first time. It is so beautiful, I am very moved," Dr Roe added.

The manuscript was found last summer at the Molesworth St Aubyn family house at Pencarrow, Cornwall.

The family knew it had a Beethoven manuscript but did not realise it was an unknown work. It had been in their home since it was written for a young English traveller, Richard Ford, nearly two centuries ago.

Ford inscribed the score: "This quartette was composed for me in my presence by Ludwig v Beethoven at Vienna Friday 28th November 1817 Richard Ford."

Its discovery and content has been a secret - even from the musicians - until the performance on Thursday.

Beethoven's middle years were his most productive

Cellist, David Watkin, said: "It's fascinating for us as musicians to be playing something for the first time in hundreds of years.

"It's like a miniature, but it's a complete piece which is very interesting."

Simon Maguire, another Sotheby's expert, said the work came after a barren period for Beethoven, just at the start of a flurry of late compositions.

"This piece packs an awful lot into a short space. It's concentrated. It sounds as if we are already in the development section of a piece," he said.

But, he added, the plaintive tenor of the composition speaks of the depressed state of Beethoven's late work and mind.