So where has Haydn's setting of Psalm 26 been all this time? Well, at home with Basil and Noel Mary Williams, who would invite friends round to sing it in their living-room. Now at last, with the manuscript up for sale at Christie's on 29 June, scholars will be able to examine a treasure which was unknown for nearly 200 years. Inscriptions on the score show it to have been a gift from Haydn to Cecilia Maria Henslowe, daughter of the distinguished violinist Francois- Hippolyte Barthelemon, who emigrated to London and put Haydn up on both of his visits. The manuscript came into the possession of Mrs Williams, who died in 1988, after she had completed her course as a violinist at the Royal Manchester College of Music in the late 1930s. 'It was a gift from a great aunt,' says Basil Williams, a former Admiralty official. 'How it came to be with her we had no idea. Although we were keen choral singers, we never sang the Psalm in public.' Christie's hopes to raise at least pounds 15,000 from the sale, a large proportion of which will go towards creating an award in Mrs Williams' memory at the RNCM.