The band were known to have been inspired by the sound of a malfunctioning Mellotron loaned to Tim Smith by Planet Mellotron coordinator Andy Thompson. The Mellotron is used extensively on the Spratleys Japs recordings. (It has since been repaired).
The band's original lineup was Tim Smith (bass guitar, vocals, Mellotron), Joanne Spratley (vocals, flugelhorn, Theremin), Heidi Murphy (electronics devices and synthesisers), Mark Donovan (guitar) and Viv Sherriff (drums). Murphy, Donovan and Sherriff were allegedly members of a band called the Rev-Ups, which initially formed near Mexico but subsequently moved to the New Forest area of England. (As Spratleys Japs have never played live and the Rev-Ups members have not been seen in public, it's possible that both they and the original band are fictional).
The band released one album - 1998's Pony - and one single - 1999's "Hazel". Both of these were released on Smith's own All My Eye And Betty Martin Music label. There have been no further releases since then.
Joanne Spratley went on to work with Christian Hayes' project MIKROKOSMOS.
In autumn 2016, Joanne Spratley organized a Spratleys Japs concert in Brighton. It took place November 19th and was billed as "Spratleys Japs Performed Live". The concert did not feature Tim Smith, who remains unable to perform following his 2008 stroke and heart attack (although he attended as an audience member) but did feature Spratley plus musicians drawn from various Brighton bands including Clowwns, Crayola Lectern, Muddy Suzuki and Heavy Lamb.
The concert led in turn to a full revival of Spratleys Japs featuring the 2016 lineup, with assorted concerts taking place in England during 2017, including a small tour.