The MK X was easily the most sophisticated Jaguar saloon yet. It had the triple carburetor 3.8 liter XK engine from the E Type, power steering as standard and fully independent suspension, the quadruple damper rear and also fitted to Jaguar’s new sports car. Smooth and rotund in styling with a girth of 6ft 4in (1.93 m), it was the widest British car you could buy. Its new monocoque shell was as well appointed inside as luxury saloons costing twice the price, featuring walnut trim, leather seats and even picnic tables. As desirable as it seemed, the Mk X was the first Jaguar to get a less than warm reception from the Press. Many thought it was simply too big to be practical in the UK, while others criticized its power steering, uncertain brakes and shapeless seats that allowed their occupants to slide around too much on corners. This gave a false impression of the Mk X, which actually handled well for its size. Certainly its ride was excellent. The 4.2 liter version that came along in 1964 had more torque for better acceleration, and much improved power steering.
The automatic gearbox was more responsive, too, and for the few drivers who ordered the manual version there was now synchromesh on all the gears. The 420G of 1966 had only very minor detail styling changes. Lengthened and embodied, the Mk X/ 420G became the chassis for the big Daimler DS 420 limousines that lasted into the 1990s.