Birmingham composer and horn-player Stephen Roberts will give the premiere of his completion of an unfinished concerto by Mozart at Worcester Cathedral on Friday night.

Known as the Horn Concerto no.0 in E-flat, the concerto was sketched by Mozart in 1781. It has long been known in fragmentary form, with the second movement performed and recorded on its own under the title Concert Rondo over the last 50 years.

Harborne-based Mr Roberts, who is professor of orchestration at the Royal Military School of Music in Kneller Hall, Twickenham, has made a completion of the two-movement work making use of newly-discovered fragments, including a 60-bar gap in the second movement, which have come to light and been published in America over the last 15 years.

A founder member of the Fine Arts Brass Ensemble, Mr Roberts now concentrates on composition, with a major commission recently premiered by the National Orchestra of Wales in Cardiff. He is the former principal horn player in the English Symphony Orchestra, with whom he will perform the concerto, directing the orchestra as well as playing the solo part.

Preparing a performing edition involved filling in a number of small gaps as well as orchestrating some passages. Mr Roberts said that he often uses Mozart as a model in teaching orchestration: “He’s so clear, and writes so well for the orchestra,” he said. “I’m always looking at his scores, so I felt quite within the idiom when I came to take this on.”

The performing edition is published by Mr Roberts’ own company Tanglewind, originally set up to publish compositions and arrangements for Fine Arts Brass, which also published Elgar’s lost choral setting of The Holly and the Ivy after it was rediscovered in the 1970s.