Jaguar Mk X and 420G: the biggest Jaguar of them all (1961–1970)

Every Jaguar list has its giant. The Mk X of 1961, the Jaguar mk10 in a thousand classified adverts, was the widest car Britain had ever put into production: a limousine-sized saloon carrying the E-Type’s engine and independent rear suspension, aimed at America, renamed 420G in 1966, and today the great undervalued heavyweight of the classic Jaguar range.

Built wide for America

Sir William Lyons drew the Mk X for the market that paid Jaguar’s bills. American buyers wanted presence, and the Mk X delivered it with a 6ft 4in beam, four headlamps and a cabin that seated five in armchair comfort behind picnic tables. The engineering matched the theatre: a unitary shell when rivals used chassis, the E-Type’s 3.8 triple-carb XK engine, and the same independent rear suspension, making the biggest Jaguar also its most sophisticated. “New grace, new space, new pace” ran the advertising, and for once the copy underclaimed.

Mk X to 420G: one car, two names

The 4.2 engine and all-synchromesh gearbox arrived in 1964, fixing the original’s gruffest edges, and in 1966 the car was facelifted into the 420G: slimmer grille bar, a chrome side strip, padded dashboard top. Nothing structural changed, which is why the market treats Jaguar Mk10 and 420G as one family with one price band. Production wound down in 1970 after some 25,200 cars, and the name’s spirit passed to the long-wheelbase XJ that followed; the 420G’s floorpan lived on for two more decades under the Daimler DS420 limousine, the trade’s hearse and wedding car of choice.

The other 420: the compact impostor

Jaguar’s 1966 naming shuffle created a permanent trap: the plain 420, sold alongside the 420G, is a different and much smaller car, an S-Type (itself a development of the Mk2) wearing the big car’s four-lamp face. It is a fine machine, quicker-steering and city-sized where the G is vast, and many buyers actively prefer it. But listings muddle the two constantly, so the first question about any “Jaguar 420” is which one. This page’s auction statistics span the Mk X, the 420G and the compact 420, which is exactly how the market encounters them.

What a Mk X is like to run

Driven, the Mk X shrinks less than you hope and charms more than you expect. The XK six pulls the near-two-tonne body to motorway pace without strain, the ride is deep-pile, and the independent rear gives composure no American rival of the day could match; only parking reminds you of the width, constantly. Running one is classic-Jaguar ownership at its most affordable to buy and least affordable to neglect: mechanical parts are shared with E-Types and XJ6s and cheap for what they are, but thirst sits in the low teens per gallon and any structural rust multiplies across acres of steel.

The limousine trade and the long tail

The Mk X’s scale gave it a working afterlife. A factory partition option served the formal trade from new, undertakers and wedding fleets ran 420Gs for decades after production ended, and the floorpan’s second career under the Daimler DS420 kept parts and specialists in business into the 1990s. Period celebrity helped the image along, with the big Jaguar a fixture outside 1960s casinos and film sets; today the same presence makes surviving cars favourites for period drama work, and a 420G with hire-fleet history is nothing to fear if the structure survived the mileage.

Buying a Mk X or 420G today

Body first, always: sills, floors, wheelarches, the rear radius arm mounts and the boot floor rot expensively, and because values stay modest, many survivors carry deferred welding. The interior’s timber and leather acreage is the second cost centre, lovely when good and ruinous when not. Mechanically the XK engine and Borg-Warner automatic are tough and known; check the rear suspension cage and brakes as on any independent-rear Jaguar. Buy the best body and cabin available and the drivetrain will rarely frighten you; the Jaguar clubs’ big-saloon registers know most surviving cars individually, which makes history checks easier than the model’s rarity suggests.

Values: maximum Jaguar, minimum money

A usable Mk X costs £8,000 to £12,000 and a good one £12,000 to £20,000, which per foot, per cylinder or per pound of presence is the cheapest route into serious 1960s Jaguar ownership. The same money buys a middling Mk2, a car half the size with twice the following. Scarcity is on the big car’s side, survivors being genuinely rare, and the 1960s revival has begun to notice. For the patient buyer with a long garage, the giant remains the bargain of the range.

More photos