The first Sovereign was a badge-engineered version of the Jaguar 420 saloon, which was itself based on the Jaguar S-Type. The 420 and Sovereign differed from the S-Type in having a revised four-headlight nose reminiscent of the Jaguar Mark X and a 4.2 litre version of the straight-six XK engine. The main external difference between the 420 and Sovereign was the traditional Daimler fluted radiator grille. There were thoughts of fitting the Sovereign with the Daimler 4½ litre V8 engine as used in the Majestic Major but as this significantly outperformed the Jaguar XK unit and would have led to the Sovereign outgunning the Jaguar 420 the Jaguar hierarchy did not pursue the idea; the Jaguar badge was meant to be more sporty than the Daimler one.
The front-end styling of the Daimler DS420 limousine introduced in 1968 shared a family resemblance with a Daimler grille mated to a four headlight nose.
The 420/Sovereign range began to be replaced by the Jaguar XJ6 in September 1968. The Jaguar ceased production in December 1968, the Daimler remaining in production until July 1969.