After series production began in 1988 the Javelin/320 combination accounted for about one third of Duple's coach output.

The 300 was introduced two years after the coach versions of the series and was available on 11 m Dennis Javelin, Leyland Tiger and Volvo B10M chassis, selling in small quantities only.

[2] Duple had struggled with a declining market share throughout the 1980s and the business was closed down at the end of the 1989 season.

In the event these plans were thwarted by declining economic conditions which limited the demand for new coaches.

A single batch of 25 12-metre Leyland Tigers was bodied at Scarborough in 1991 and sold through the Yeates coach dealership as the Plaxton 321, but no further examples were built.