There is no pleasing some car buyers. They whinge because the new model does not look like the successful, popular, elegant, sporty but practical old one — or they whinge because it does. Jaguar has a real problem with this. When it launched the S-Type, which looked little like its elegant XJ sibling, that dichotomy of opinion was rife and it was then sub-divided because many people thought the S-Type’s nose, with its distinctive, classic radiator grille, looked terrific, but that the rest of the car did not.

The compact X-type does carry elements of the XJ likeness but some critics feel that it doesn’t quite work on a smaller scale. That is Jaguar’s “damned if you do, damned if you don’t” situation.

So when it came to updating the XJ it was a tough call for the Jaguar designers, who, mindful of the importance of the car to the company’s financial future (and possibly to their own) needed to get it right. They have.

The new XJ may look at first glance much like the old one, but placed side by side it is a design of today that suddenly makes the previous model look decidedly passé. Its waistline is higher and so is its roof; it is a little longer, a little wider; the previous model’s enormous rear overhang is reduced; and the effect is to create a car that has stronger, more balanced proportions.

On sale next spring (we have not driven it yet) but on display at next week’s Paris Motor Show, the new XJ looks set to demonstrate that design evolution can span more than three decades and still look convincingly fresh and not just a retro rehash. But the attraction of the new XJ is not just its exterior styling.

It has evolved as a technological tour de force with, like its competent rival, the new Audi A8, a weight-saving aluminium body (the XJ is about 200kg, or 440lb, lighter and much stiffer than the old one) and systems which include voice-controlled navigation; screens in the rear of the front seat head restraints; four-zone climate control, adjustable pedals and safety technology which senses the presence, position and size of a front seat passenger to determine the correct airbag energy level.

There is a choice of engines, from the superb 4.2-litre supercharged V8 of the R version, to a 3.0-litre V6. But there is no diesel, a surprising omission in a car of this class. All XJs get a smooth ZF six-speed automatic gearbox. Air suspension lowers ride height at speed, and computer active technology helps provide the sort of ride and handling package that singles out big Jaguars in a discerning market sector.

The interior of the new XJ is what is expected — lots of leather, plenty of wood and the traditional “ski-slope” centre console. A new trim is piano black, “a highly polished finish inspired by the deep lustrous sheen of a concert grand piano”, as Jaguar’s poets’ corner puts it. An electronic parking brake similar to that fitted to the S-Type, is standard. There is more room for everyone but, significantly, rear-seat leg-room has been improved.

Jaguar stresses that it was not trying to make the new XJ the roomiest in its class — good news, because a Jaguar’s strength has long been its cossetting interior that makes driver and passengers feel they are almost strapping the car on, not merely getting into it.

Will the new XJ date in a few years and suddenly appear to be a 1968 concept struggling in the 21st century? I very much doubt it — particularly if it performs as impressively as it looks.