The Double Piano was the rather extravagant whim of the Parisian firm of Pleyel, whose instruments were the favourites of composer/pianists such as Chopin, Grieg, Debussy, Saint-Saëns and Stravinsky. The company's success led them to invest in experiments, resulting in 1890 with a Double Piano and later with their version of the Pianola. 

Although not the first company to experiment with building two pianos into the same frame, Pleyel (who patented it as "Duo-Clave") was by far the most successful and produced the largest instruments. A very small number of Double Pianos were manufactured in the 1890s, and it was one of these first models (2.46m/8 feet) which Nettle & Markham encountered when they were invited in 1989 by the BBC in Northern Ireland to give the first public performance on a newly restored instrument in County Down.

Their own Double Piano, however, is a larger "concert" model which Pleyel made in the 1920s and was one of the last to be made; it is therefore very much a "modern" piano and the same age as the two Steinways in their London studio. It was purchased in 1993 from a private owner in Paris, having  originally been housed in the Théâtre du Châtelet in Paris. The instrument can be best described as two overstrung pianos in one rectangular case (measuring 1.53m/5 feet - the normal keyboard width - by 2.90m/9 feet 7 inches), with a keyboard at each end, a combined soundboard and one large lid to reflect the sound of both pianos to the audience.

By extensive research in Paris Nettle & Markham have located only six surviving instruments of this size, and theirs is the only Double Piano in the world being used for concert tours by an international piano duo. It is pictured in two books: "Piano" by David Crombie (Outline Press Ltd 1995) and "The Piano" by Jeremy Siepmann (Carlton Books Ltd 1996).