Mozart music sheet for auction.

ONE of only two surviving manuscript leaves from one of Mozart's greatest compositions has been found in a private collection.

It is the cadenza for the first movement of the Sinfonia Concertante in E flat for Violin, Viola and Orchestra, K364, the 1779 masterpiece that catapulted him into the ranks of the world's greatest musicians.

It is the most important single leaf in the composer's hand to have appeared on the market for decades.

Although a single sheet, it comes from Mozart's greatest work for the violin and what is widely regarded as the greatest work by anyone for the viola.

It is due to be auctioned at Sotheby's in London on Tuesday and is likely to beat the auctioneer's pound £100,000 estimate.

The reverse of the sheet will particularly interest scholars as it bears the playing parts for two horns, again in Mozart's hand, for two unidentified pieces.

Simon Maguire, senior specialist in Sotheby's music department, said: "The Sinfonia Concertante is not only one of Mozart's greatest works, it is also the key work that saw the young composer attain the level of musical accomplishment that has defined his reputation ever since."

The Sinfonia Concertante was composed when Mozart was 23 years old.

All that survives of the original score are the two leaves containing the two cadenzas and it is one of these that has now emerged.