Complex sentence: In 1997, Brian's 1951 opera in eight scenes "The Cenci", based on the 1819 play by Percy Bysshe Shelley, was premiered in a concert performance at the Queen Elizabeth Hall, London, by the Millennium Sinfonia, conducted by James Kelleher.
Split into simpler sentences: In 1997, Brian's 1951 opera "The Cenci", based on the 1819 play by Percy Bysshe Shelley, was premiered in the UK. The opera, in eight scenes, was performed in London by the Millennium Sinfonia, conducted by James Kelleher.