Jaguars, like a fine wine, improve with age. The XK8, far from becoming belligerent and incontinent in its old age, has been steadily refined over the years. The XJ saloon is now the car it always should have been, too. And the S-Type, after a wobbly start, has matured into a distinctive alternative to the predictable German offerings.

This latest edition to the range, the 2.7-litre twin-turbo diesel model, coincides with a further round of subtle changes to the styling and improvements in overall quality.

The retro looks are still a little too Morse for some people, although the latest revisions tighten up the shape usefully. It’s unmistakably Jaguar and in Sport guise with 18-inch wheels and fussy chrome detailing removed, it’s quite muscular in profile.

Now it has the diesel engine that is mandatory to compete in the tough executive segment, how does the S-Type stack up against its Germanic rivals, the BMW 5-series, Mercedes E-Class and Audi A6?

Let’s deal with that styling issue first. Jaguar is one of the oldest automotive brands still in existence, and that brings with it a great deal of historic baggage that has to be incorporated when penning a new design. There’s no questioning that the S-Type looks like a Jag from every angle, but thankfully much of the fussy detailing has been simplified in the recent restyle.

There are two distinct styling characters on offer. The standard models feature chrome highlights on the bumpers, grille, boot lid and around the window line, which serves to create a conservative, almost staid image. The alternative arrives under the Sport badge, which carries with it larger 18-inch wheels, and replaces the chrome with body-coloured trim. It’s a simple stylistic change, but works to reveal a sportier nature that feels more in keeping with Jaguar history, and knocks twenty years off the age of any prospective owner.

Inside, there are new technical finishes to the dashboard that contrast well with the thick, quality leather of the centre console, and new dials with classically-styled graduations and numerals. The deep dash is covered with an almost foam-like material that seems to stretch for a country mile towards the base of the windscreen, but rather than impinge on passenger space it instead promotes a cosy and secure ambience. The view from the driver’s seat through the windscreen has an almost Cinemascope quality to it. It’s all very, well, Jaguar.

Some of the switchgear is desperately close to pension age, with the electric window and mirror switches in the door more than a little reminiscent of those used in Fords twenty years ago. The trademark J-gate transmission layout is also close to retirement, in our opinion, with the tiptronic functions of the competition offering a less clumsy selection of cogs.

That said, it’s a comfortable place to be, with the big seats offering plenty of support and a wide range of electric adjustment (adjustable pedals are on the options list, too). The column itself sports a greater range of travel than its rivals, allowing the flexibility to adopt any driving position you wish, and the column retracts when you remove the ignition key to make way for a dignified exit. A memory function is standard on the Sport, and maintains the position of the seats, mirrors and steering column for two drivers.

Rear seat accommodation is compromised slightly by the falling roof line, and boot space is rather shallow and restricted by the narrow opening, but four MD wallahs and their golf clubs will still fit comfortably.

The optional satellite navigation of our test car replaces much of the button confusion in the centre console with a touch screen system, but there are still dedicated buttons for temperature and other climate and audio functions. We much prefer these touch screen systems to the twiddle-and-push alternatives offered by BMW’s iDrive and Audi’s MMI. Park your average 60 year-old company director in the front of a BMW with the task of finding Radio 2 and you could be in for a long wait. With the Jaguar’s system, it takes only a few exploratory stabs of the finger to summon Terry Wogan to the car’s interior.

Despite the numerous changes to the interior over the years, there’s still very little in the way of oddments space. While the overhead console has a pop-down sunglasses holder, there’s nowhere to store a mobile phone or much else.

Twist the key, and somewhere in the distance an engine stirs. Noise and vibration suppression are excellent, with only a muted growl and a few hundred rpm showing on the rev counter to offer any clue as to whether the engine is running.

There’s no handbrake to release; it’s replaced by an electronic system that automatically engages when you remove the ignition key and releases when you select a gear. One less thing for tired execs to worry about.

On the move, the Jag is quick to impart its relaxed character. Even the most furrowed of brows will be soothed by the supple ride, and this is the Sport suspension, remember. The gearbox swaps ratios imperceptibly and the power plant never betrays its oil-fired nature.

It’s all very relaxing. Enjoyable, even. And we were unable to detect a single buzz or rattle from the interior trim.

Things are a little less accommodating when it’s time to press on, however. The twin-turbo 2.7-litre V6 engine is capable of delivering 206bhp at 4,000 rpm and 320 lb/ft of torque at a slow-spinning 1,900 rpm and, while that’s enough to hustle the big cat to 60mph in 8.2 seconds and on to 141mph, there’s nothing very urgent about the way that power is delivered.

The automatic transmission needs determined encouragement, usually by shoving the loud pedal into the carpet, before it’ll change down a cog or two. The alternative is to use the J-gate, but since this requires the shifter to take a lengthy journey from one side of the gate to the other, it’s a practice that’s easy to grow tired of. However, once you’ve persuaded the gearbox to work on your side, progress is quite rapid, during which refinement levels never slip.

It’s a shame the transmission isn’t more co-operative, since the S-Type is more than capable of picking and holding a sporting line through a series of bends. With a less obstructive gate or, ideally, a tip function, the S-Type would lose much of its point-and-squirt nature and become more of an all-rounder.

Against its rivals, it’s well appointed, with folding electric mirrors, electric memory seats in perforated leather, automatic headlights, trip computer, single-slot CD player, metallic paint and 18″ alloy wheels.

To the on-the-road price of £31,670, our test car added six-speed automatic transmission (£1,380), parking radar (£610) and DVD-based satellite navigation (£2,000), bringing the total to £35,660 – that’s around £2,000 cheaper than a similarly-specced Audi A6 or BMW 530d SE. We hear that Jaguar dealers are keen to offer a deal, too.

It’s also cheap to run, with insurance at an incredible group 14 (against 17 for the BMW, 16 for the Audi) and economy over the combined cycle of 36 mpg. The one chink in its budgetary armour is depreciation, retaining only 48% of its purchase price after three years/36,000 miles. Fleet buyers should note that the auto version doesn’t currently meet Euro IV emissions.

Against its rivals from Bavaria, Stuttgart and Ingolstadt, it’s clearly a very different machine. It doesn’t try to be something it isn’t, and instead tries to win you over with its own personality. After a hard day in the boardroom, the Jaguar will be waiting for you in the car park, like an old Spaniel with your slippers and the evening newspaper.

It’s ironic that, for a brand that plays much on its sporting pretensions, the diesel-fired power plant suits the Jaguar’s character far better than its petrol equivalents. With a relaxed yet torquey nature, it’s the engine the S-Type has been crying out for.

The 2.7-litre twin turbodiesel engine is the power unit the S-Type has been crying out for. Excellent ride quality, even from the Sport suspension. Auto ‘box reluctant to kick down, and power delivery generally less urgent than its rivals. Some concern over recycled switchgear, but touch screen system far better than iDrive clones. Good value, too. If you’re happy with the image (not everyone is), it’s a very credible package.
Our verdict: Our verdict: 4 stars out of 5