IT'S a brave car company that messes with a winning formula. Much more sensible to take what buyers like and make it better.

So it's no surprise the new Jaguar XF - and it is properly new, with a changed body and new engine - looks so much like the car it replaces.

Buyers loved the old one, so they surely will be bowled over by a replacement that echoes the styling cues of the original XF, inside and out.

But it's much more than a mild reworking of a formula that has proved a past success; lots of aluminium in the newcomer brings useful weight saving, despite more room inside a car that now actually measures a fraction shorter and lower than before.

Under the bonnet of most new XFs beats a new Ingenium diesel engine produced at a vast (and vastly expensive) new factory in Wolverhampton and fitted to other models in the Jaguar and Land Rover ranges.

You can, but probably won't, buy your new XF with a powerful petrol engine (the States and China will love 'em) but those 380 underbonnet horses can cost up to £49,995.

The XF range starts at £32,300 for a lower powered (163hp) diesel and you can't think most buyers would want for more - unless it's the same basic engine, still with 2.0-litres but producing a bit more poke.

It's the unit fitted to this particular car and the 180bhp on tap produce a car comfortably fast enough for anyone the right side of a racer in disguise. Equally impressive, it managed 46mpg on test - the sort of figure you could only dream of a decade ago in a car this large and capable.

Jaguars have always been no bigger than necessary inside and the XF continues the tradition, even with added knee, leg and headroom in the rear seats. Big enough for long range comfort but hardly limo-like.

This cabin intimacy flows through to the driver, confronted by a set of instruments designed to be clear and concise (not always the case) and air vents and transmission selector than unwind theatrically at ignition on and vanish as smoothly on switch off - an XF party trick carried over from the original cars.

Also continued (and another Jaguar long term trait) is a delicate compromise between ride comfort and a sporty feel. Jaguar's rivals (are you listening Audi?) sometimes get this wrong for British roads, leaning too far towards the rock solid.

The XF benefits from its UK-based engineering team and wafts its way over the worst our roads can throw at it, yet still feeling alive and alert in an executive car sort of way.

This executive motor also impresses in the equipment stakes, with the top Portfolio version including a crisp looking satellite navigation system on a big touch screen, lane departure warning, cruise control with automatic speed limiter and wifi, DAB and iPod integration.

Take care with the options list though (think Audi again) as the car's £39,050 list price was pushed over £50,000 with add-ons like sliding glass sunroof (£950), adaptive LED headlamps (£1,225) and parking assist with cameras (£1,620).

Sadly, the test was halted early after an engine warning light on the dash prompted a journey to the nearest Jaguar dealer, where a faulty emissions injector was diagnosed. With the prospect of the car defaulting to limp home mode it was collected by trailer and my time in the XF ended prematurely.