With the convertible stealing the summer limelight, BMW has completed the 6 Series range with a Coupe version just in time for the harsher winter weather.

The Coupe also sees the introduction of M Sport derivatives and a new twin-turbocharged diesel.

Wider and lower than before, the new car is certainly attractive, if not a natural beauty. This I think is enhanced by the new M Sport specification that's launched at the same time and includes an M Aerodynamic body kit.

The kit includes deeper, more aggressive front and rear aprons with chunkier side skirts and I particularly like the high, defined shoulder line and the rear styling. The way the rear light clusters fold into the rear quarters looks sleek.

The 6 Series coupe might have a roof, but inside it feels the same high quality finish as the convertible. The 6 has to have one of the most attractive, driver-focused interiors that BMW has produced. I really liked the sweeping dash section that can be optionally trimmed in leather (recommended but expensive at £1,000) and runs along the centre console.

The Coupe is available in 640i, 640d and 650i versions and all are well-equipped with prices starting at £59,565. Standard equipment includes 18-inch alloy wheels, dakota leather trim, eight-speed Sport automatic transmission, BMW Professional Multimedia Navigation system, xenon headlights, two-zone air-conditioning and front and rear park-distance control.

There's also plenty of room in the front and a fine driving position. Shame it's at the expense of rear space but at least there's still plenty of headroom for all. There's also a practical boot with ski hatch.

According to BMW, 93 per cent of the last generation 6-Series were powered by diesel engines and 97 per cent left the showroom in Sport guise. I had the chance to drive what BMW expects to be the top-seller, the £66,745, 640d M Sport. Starting my journey in Wales, I had a 400 mile route home to check out BMW's latest car.

The 640d is powered by what could be the sportiest diesel engine yet; a new 313bhp, 3.0-litre twin-turbocharged, six-cylinder engine that backs up its sportiest diesel claim with a top speed of 155mph and 0-62mph acceleration in just 5.5 seconds.

Considering this performance the 145g/km Co2 emission figures are impressive, meaning buyers will pay just £130 a year car tax.

The coupe feels sporty enough to justify its M Sport tag with the throttle and brakes crisp and precise while its composure over the twisty Welsh test route impressed. My car was also fitted with BMW's Optional Adaptive Drive, which adds electronically controlled dampers and roll stabilisation to the already impressive Dynamic Drive Control system.

A costly £3,400 option, this system means you can set the 6 Series up just how you like it; with a simple push of the rocker switch next to the gearchange, you can choose a variety of sporty or comfort settings. I found the default option for this car was the sport setting, as it felt more dynamic in this mode.

Yes, the 640d M Sport has a harder ride, but it doesn't fall apart, even on the tautest Sport+ set-up. Add in the stiffer bodyshell and the 6 Series generally does comfort and dynamism well, even on the M Sport's 19-inch alloy wheels.

The 640d's eight-speed gearbox felt slick and smooth, working best in the twisty stuff on the steering column-mounted paddles.

The BMW Professional satellite-navigation has a massive 10.2"screen which dominates the dashboard, but on the way home its regular updates got me out of at least two serious jams.

The only downside is the steering, which maybe could do with a little more feel. This isn't helped by the over-thick rim of the M Sport steering wheel.

To sum up, the 640d is an accomplished and fast grand tourer, fitted with a peach of a diesel engine. It's much more comfortable than you'd expect an M Sport specification car to be. Yet, it still has the balance and handling you'd expect of a BMW.