The XJ40 used the Jaguar independent rear suspension arrangement, and featured a number of technological enhancements, such as electronic instrument cluster.

Ford halted development of the saloon, termed XJ90, and proposed to install its new engine and front and rear ends onto the centre section of the XJ40 model; however, the V8 was not ready.

Due to the 1973 oil crisis and problems at parent company British Leyland, the car was continually delayed.

The protracted development time meant the car dated much quicker than its rivals, and it was quickly superseded technologically by the E32 BMW 7-Series (1986), the Lexus LS400 (1989), and the W140 Mercedes-Benz S-Class (1991).

The United States safety regulations allowed the form-fitting composite headlamps in 1983 for the model year 1984 onward.

During the 1990 model year refresh, the United States-specified XJ40 received the composite rectangular headlamps for entire trim levels.

The United States headlamps have two separate reflectors for low and high beams behind the slightly bulbous plastic lens.

The bumper is a visually distinct black-rubber-covered bar that runs the full width of the car, and incorporates the sidelights and indicator lights.

Until 1990, cars were fitted with an instrument binnacle that used digital readouts for the ancillary gauges, but still featured an analogue tachometer and speedometer.

Instrumentation included a vacuum fluorescent display named the Vehicle Condition Monitor (VCM), which contained a 32x32 dot-matrix screen capable of 34 functions.

The VCM was able to alert the driver of bulb failure, brake pad wear, unlatched doors/boot, and low coolant level.

The base XJ6 of the model range was modestly equipped; extra-cost options included alloy wheels, anti-lock brakes, air conditioning, leather upholstery, and an automatic transmission.

[7] These vehicles started life as a SWB body that was then taken away from the standard production line and stretched by Project Aerospace in Coventry, before being returned to Castle Bromwich plant for paint before being finally assembled on the production line at Browns Lane under the direction of Jaguar Special Vehicle Operations.

Jaguar devised Insignia: a bespoke service for the XJ40/XJ81 and XJS, where prospective owners could specify special paint, trim, wood, and wheels at additional cost in any given combination.

All of the interior trim was done in leather (two-tone colouring being an option), opposed to the leather-vinyl combinations used on regular-spec cars.

These XJ40s were badged as Police Special (PS) vehicles and received mainly plastic interiors devoid of luxury fittings.

[14] The XJR, introduced in 1988, was a high-performance model that was finished by the Oxfordshire-based JaguarSport company, a dual venture by Jaguar and Tom Walkinshaw Racing (TWR) team, at TWRs Kidlington-based factory alongside the XJ220.

The XJR differed cosmetically from other XJ40 models with its body coloured bodykit, consisting of new front and rear valances and side skirts, all from fiberglass, a black grill with a JaguarSport badge in it and unique Speedline alloy wheels with wider tyres.

Later models had ducting fitted to the front valance to feed cool air directly to the brake discs.

In 1991, the appearance of the XJR changed when it switched to the rectangular headlights of the Sovereign model and was fitted with a different design of bodykit.

Given the model code XJ81, the XJ40-based XJ12 and Daimler Double Six were introduced at the Amsterdam Auto Show in February 1993 and powered by a 6.0-litre version of the Jaguar V12 engine.

The Daimler Company-branded cars represented the highest trim level, and were sold as their Vanden Plas model by Jaguar dealers in the United States.

Cosmetically, it differed from other models with its fluted radiator grille surround, boot-lid plinth and detail finishes.