The 420 and Sovereign differed from the S-Type in having a revised four-headlight nose reminiscent of the Jaguar Mark X, and being powered by a 4.2-litre version of the straight-six XK engine.

The main external difference between the 420 and Sovereign was the traditional fluted radiator grille on the Daimler.

Once again, it was externally virtually identical to its Jaguar source car with the exception of its fluted grille and Daimler badging.

The Series III XJ6 range, which was released in 1979, was visually distinguished from the Series II by its new thicker bumpers, the removal of separate "quarter-light" windows from the front doors, and a revised rear roofline featuring a slightly more angular c-pillar.

A two-door coupe variant of the Sovereign Series II, utilising the shorter wheelbase platform, was offered from 1975 to 1977.

[4] Unlike the Jaguar, the twelve-cylinder Daimler had the same radiator grill as its six-cylinder sibling, and externally only the badges distinguished them.

On a 4 inches (100 mm) longer wheelbase, this model also received a black vinyl roof to set it apart.

[3] When Jaguar re-engineered the XJ40 (the successor to the Series III) to take a 6.0-litre version of the V12 engine, under the model designation XJ81, a new Double-Six was also produced, being manufactured between 1993 and 1994.