Britten writes to Imogen Holst on 10 Dec 1955 that he completed this piece on a recent 'free morning'. In the days leading up to 10 Dec, Britten's engagement diary was free only on 8 and 9 Dec. See Philip Reed, Mervyn Cooke and Donald Mitchell, eds., Letters from a life: the selected letters of Benjamin Britten (London: Faber, 2008), vol. 4: 1952-57, pp. 361-366, esp. n2.
The piece was written for James Blades (1901-1999), British timpanist and percussionist. He began working with Britten in 1953 when he joined the EOG orchestra.