In 1986, three four-car prototype trains were built for the Central line. They trialled new technology and interior design. Each had its own colour; red, blue and green. As well as extensive testing, the prototypes saw brief spells of passenger service on the Jubilee line in 1988 and 1989.
The public consultation results show that the blue prototype was the favoured and provided the core design basis for the 1992 Stock that was built for London Underground's Central line and for the Class 482 which was built for Network SouthEast's Waterloo & City line.