BMW 640D Grand Coupe

Engine: 3.0 litres, six cylinders, turbocharged
Top speed: 155mph
Price: £62,085
Power: 309bhp at 4400rpm
Fuel/CO2: 50.4mpg, 148g/km

Some cars you just have to drive before they make sense, and BMW’s new four-door Grand Coupe is a fine example. On paper its a 6-series coupe, stretched like a strip of liquorice until its all but as long as a 7-series limousine. But what’s been done with that extra space? I sat in the back and reckoned there was less room than you’ll find in a 1-series hatch.

But over the course of a week and many hundreds of miles, and despite several other choices, I found myself increasingly unwilling to be parted from it. I found myself liking it for all sorts of reasons that don’t usually register with me at all: its looks to name but one. I’m interested in what cars do, not how they appear but I still caught myself gazing at the BMW more than any other mass-produced car I can recently remember.

This didn’t happen when I first drove its very close cousin, the 6-series coupe, but that extra 115mm stretch between the wheels and the addition of a B-pillar has turned a handsome coupe into something I had trouble tearing my eyes from. It’s not a beautiful car like the original Mercedes CLS, but it is exceptionally handsome, especially in profile. And I can’t recall when I last felt that about any BMW.

It’s good to drive, too. Together it and I did two major journeys: 300 miles on motorway to and from a business appointment, then 300 miles mainly crosscountry for a Goodwood track day. What better ways to reveal its true character?

On the first journey it was better than a 7-series: quieter and far more deftly suspended. I left it in ‘D’, dialled up the most efficient mapping modes for engine and gearbox and drove from the Wye Valley to Cambridge with both car and driver on autopilot. On the return I was caught in vicious traffic but swaddled in deep seats and entertained by a vast array of digital radio stations, I was surprised by how little bothered I was. Total fuel consumption? 42.2mpg.

The second journey was, if anything, more instructive still. With almost three metres between the front and rear wheels, this was never going to be an exactly nimble machine, but what it lost in the corners, it soon regained on the straights. BMW engineering has brought us to a point where it can put a 3-litre diesel engine in a car as vast as this and still coax it past 62mph in 5.6sec, yet still prove sufficiently frugal to return over 50mpg. Ten years ago, a petrol 645i was slower to accelerate yet used almost exactly twice the fuel. Despite a relatively modest 70-litre fuel tank, it dispatched both journeys without requiring a fuel stop.

I don’t know why it took BMW so long to come to the four-door coupe party. Unlike Mercedes, which invented the category with the CLS back in 2004, Porsche with its Panamera or Audi with the A7, BMW didn’t need to design an all new car, it just had to elongate an existing one.

But this too provides a problem: why will anyone purchase a standard 6-series coupe any more when for just £1800 more you can have a Grand Coupe that’s better looking, practical and spacious? For BMW that is one of the nicer problems it could have.