IF one were to draw up a list of the greatest British cars of all time, by just about any criteria the Jaguar XJ6/12 would be included.

During a production run that spanned more than two decades, it was frequently acclaimed as the greatest car in the world.

However, so good was the overall package that it set new standards for the luxury car market for many years after its launch in 1968.

The story of the original XJ saloon is by and large the history of Jaguar Cars itself during its production life.

However, a delve into contemporary newspaper archives reveal a much more complex story, and nothing is as straightforward as it seems.

The origins of the XJ6/12 date back to the early 1960s, when Jaguar was producing no less than five different basic models.

At the time, it was building around 25,000 cars per year and was winning many admirers across the globe.

By this time, sales of the Mk2 were in decline, and the 2.4-litre version was being shown the way by the compact new 2-litre saloons

The MkX was a bulbous looking range-topper, at one stage the widest car ever sold in Britain.

Quite simply, Jaguar’s model range was far too complex, and if it was to survive in the long term, a policy of rationalisation and cost-cutting was the only way forward.

A plan was devised to develop a new car to replace this mid-range morass in one fell swoop, and quickly crystallised to become Project XJ4.

The engine bay was going to be more capacious than the Mk2, too; the idea being to future proof the XJ4 for the new and exciting engines Jaguar had in development.

The engines destined for the XJ4 were variants of the XK DOHC unit first seen in 1948.The engines destined for the XJ4 were variants of the XK DOHC unit first seen in 1948.

The 4.2-litre engine powertrain, both manual and automatic, made its debut in the 420/Sovereign in 1966, enough time to iron out any bugs.

Surprisingly, the triple carburettor version seen in the E-type and MkX was not offered, perhaps because something better was on its way.