Following on from Chrysler's pioneering work in the early 1960s, Bristol fitted an alternating current alternator in place of the traditional direct current dynamo, which had proven difficult to drive at high engine speeds.

Also a follow-up to previous work on the 408 was an improved safety lever to prevent anyone from putting the automatic transmission in gear accidentally.

The styling was almost unchanged from the 408, though the radiator grille was now altered into a trapezoidal shape rather than the precise rectangle of the 408.

The 409 was the first Bristol to be offered with power steering, initially as an optional extra but after June 1967 as a standard feature.

The subsequent Bristol 410 sported a central transmission shift lever, as well as a more streamlined frontal design.