Skempton was to write a piece to be performed between the Prelude from Richard Wagner's Parsifal and a Deryck Cooke completion of Gustav Mahler's Tenth Symphony.
Lento was completed in November 1990; it was premiered on 12 March 1991 by the BBC Symphony Orchestra at the Barbican Centre concert hall, conducted by Mark Wigglesworth.
The work is scored for 3 flutes, 3 oboes, cor anglais, 3 clarinets, 3 bassoons, contrabassoon, 4 horns, 3 trumpets, 3 trombones, tuba, timpani, and strings.
Like much of Skempton's work, Lento uses precomposed chance arranged sequences of chords as the basic harmonic material.
The opening section presents the "first subject" and establishes the tonic key of G minor.