Perhaps we're getting numbers mixed here - the HS125 (Hawker Siddley, later merged into BAe) was a twin biz jet, very popular in the states in the early 1980s except for the engines, RR Viper 520/620 series donks were thirsty.
Actually the HS125 started out as a De Havilland design, the DH125, but became the HS125 when De Havilland merged with various other companies to form Hawker Siddeley.
Similarly the Trident started as the DH121 and became the HS121.