It didn’t come without a price though; its massive development costs led Jaguar founder William Lyons to merge his company with BMH in order to get access to the funds necessary to put the XJ into production. Ironically, he was later said to have admitted that he would have reconsidered the move had he known how precarious BMH’s own finances were.

Jaguar had swallowed up the Daimler company in 1960 and although the firm’s car range had been discontinued, the name was still used for the range-topping Jaguar models like this Daimler Sovereign – which, in all but name, is a short-wheelbase Series I Jaguar XJ 4.2.

It’s a pretty special example; bearing an amazingly low 30,000 miles it gives a taste of how a new XJ6 would have felt back in the day, fresh from Browns Lane. In fact, we arrived at Spinning Wheel in a more modern XJ saloon – the so-called X300 model, which was in practice a major revamp of the XJ40 – and having driven the two back-to-back it’s incredible how the Series I Daimler doesn’t feel too far removed from its ’Nineties cousin. All of which neatly explains why it took Jaguar so long to replace the XJ, since the series two was a facelift of the original car and even the series three still retained a large proportion of its structure.

The interior ambience of the Series I is something Jaguar never bettered and indeed the firm stuck with the same theme through the XJ40, the X300/X308 generation of the ’Nineties and even the aluminium X350. The snug ‘cockpit’ driving position and traditional round instruments were something that gave the Jaguar a luxury feel that was very distinct from the sometimes spartan and plasticky European opposition and it was something the firm only abandoned with the launch of the very self-consciously modern current XF and XJ ranges.

Settle into the Daimler and it feels modern, with a high-set central console and a key/starter on the column rather than a separate push button, which many makers were still using. Firing up the XK engine it sounds crisp and eager, Jaguar’s twin-cam design being a world away from the plodding pushrod straight-six engines used by its competitors. The unit may have been designed in the ’Forties but two decades on was still well up to the task of powering Jaguar’s flagship model and in 4.2-litre form, as in this car, is good for some 245bhp.

Although the V12 cars are more powerful, the 4.2-litre XK-engined cars often seem more sporting in character and even in automatic form are pretty spritely. Jaguar quoted a top speed of 124mph and 0-60mph time of 8.8 seconds, which means they’re more than capable of keeping up with modern traffic and will cruise on the motorway all day.

Slipping the elegant shifter into drive the XJ oozes away with superb refinement yet feels remarkably brisk for its age when asked to hustle. The suspension can get expensive on these cars when it ages but this one gave no cause for concern. A common test is to drive slowly over a rough surface, at which point perished bushes and general ageing will reveal itself, but this Daimler was nicely composed and silent from underneath.

It’s a beautifully original car and drives well, with an interior that offers just the right blend of patina and originality. As Spinning Wheel’s Adrian Walker added; “Just try finding another”.

Engine: 4235cc
Power: 245bhp
Top speed: 124mph
0-60 mph: 8.8 secs
ECONOMY: 21mpg
Gearbox: 3-sp auto