NO ONE saw this one coming. Until now the mainstays of BMW’s range have been resolutely saloon cars and they have sold like the proverbial hot cakes. Is there room in the range for a 5-Series hatchback?

Clearly BMW thought so, because here it is: the 530d GT. A car that takes all that is good about the 5-Series saloon and wraps it up in a roomier, more practical body that mixes saloon with people carrier and even a hint of an off-roader. What is it? BMW calls it a Gran Turismo (no relation to the PlayStation game) and that’s good enough for me.

The styling takes a bit of getting used to: it’s brutal and massive from whatever angle you choose to look, but I found it growing on me during the test period and the exclusivity certainly gets you more roadside double-takes than any comparable BMW saloon.

Although it wears a 5-Series badge there’s also an awful lot of the far more expensive 7-Series saloon range to be found in the GT.

The door handles, for instance, are the same beautifully sculpted items you’ll grasp on a 750 and are much more expensive to manufacture than the standard items on the 5-Series saloon due to the technical stamping process required. But they are fitted to the 530 GT because they integrate perfectly with the swage line that runs around the bodywork.

Inside the GT’s black panel instrumentation is another direct crib from the more expensive 7-Series line. Modelled on high end hi-fi, the black surface looks cool and understated, lighting up with information when the ignition switches on. The colour ‘infotainment’ monitor is covered with a special foil that absorbs stray light and prevents reflections even in direct sunlight. Too expensive for the standard 5-Series, the GT’s cousins make do with an old-fashioned plastic ‘hood’ arrangement instead.

In fact, the cabin looks, feels and smells more up-market. The carefully chosen leathers, plastics and alloys are carefully blended with discreet ambience lighting to create a feeling of relaxation not unlike a posh night club. Designer Oliver Heilmer said he wanted to create the same kind of feeling one gets with a private jet. Not having my own personal set of wings I’ll have to take his word for it, but there’s no doubt this is one of the finest interiors to grace any BMW in recent times.

Even the controversial one-dials-controls-everything centre console has been re-thought to make the user interface more intuitive. And if you get stuck there’s a handy help function that pops up on the monitor screen to tell you what to push, prod or turn.

The cabin has acres of room, too. One of the design briefs was for a car that offered the same legroom as a 7-Series but on a body no larger than a 5-Series. Everyone who travelled in the back of the GT remarked on how much space they had.

Remarkably, given the coupe-like downward sweep of the roofline, the GT has plenty of headroom as well. The designers achieved this by using frameless doors for the first time on a BMW. Fears that this would result in more wind noise and disturbance proved groundless – clearly the door seals are top quality. Continuing the luxury jet theme, the rear seat headrests fold inwards for better head support – perfect if you fancy a kip.

Although the GT can be had with a full range of engines, including the flagship 4.4-litre V8 turbo, it is the up- rated 3.0-litre turbodiesel that will account for two thirds of all sales.

And it’s not hard to see why.

The bang up-to-date specification (aluminium-silicon alloy block to save weight, variable geometry turbo for smooth power and third generation common-rail injection for ultra precise fuelling) translates into a powerful (242 bhp at 4,000 rpm), flexible (398 lb/ft of twist from 1,750 rpm) and, above all, economical (40 mpg fuel consumption anyone?) engine that feels like the perfect fit to the GT’s inter-continental travel brief.

Make no mistake; this is one of the world’s greatest diesel engines: as quiet and refined as a petrol V6, as punchy as a V12 and as frugal as a small capacity inline four it does everything... perfectly.

And it does so in a car that inherits the 5-Series saloon’s uncanny knack of seeming to shrink around the driver when the going gets tough. Switch into Sport mode (or Sport+ mode if you really fancy some fun) and the grippy 530 GT belies its size, hustling along challenging B-roads like a well sorted driven GTi.

And here I am at the end of the test and I haven’t even mentioned the hatchback yet – nor the clever twin opening system that means you can use it like a saloon or a hatchback (oh how BMW’s R&D must have blanched when the Skoda Superb arrived a few months before the GT wearing essentially the same set-up).

The boot is plenty big enough and the hatchback certainly makes the GT a more practical day-to-day car than a saloon, but, for me, it’s what’s beneath the skin that makes this BMW special.

SPEC CHECK: Engine: 2,993cc turbo-diesel Max power: 242 bhp @ 4,000 rpm Max torque: 398 lb/ft @ 1,750-3,000 rpm Top speed: 149 mph 0-62 mph: 6.9 seconds Combined fuel consumption: 43.5 mpg CO2 emissions: 173 g/km Road tax: £175.

EQUIPMENT: Leather heated seats, 8-speed automatic gearbox with 'normal','sport', and 'sport+' settings, double glass sunroof, electric mirrors, windows, climate control, park distance radar, heads up display, satellite navigation (£1,540 extra).