BMW 740d M Sport

The performance and economy improvements have been made on this engine in several ways. Diesel is now injected at 2000psi for more efficient combustion, and Munich’s Efficient Dynamics tech means the alternator, and other power-draining ancillaries, can disengage under acceleration, allowing more of the engine’s power to be fed to its wheels.

But the most significant change relative to the old twin-turbo diesel six comes on the smaller of the engine’s two turbochargers, which has variable vanes to improve response at low revs. As a result, peak torque comes in at just 1500rpm; you get 30lb ft less twist in a 535d, and not until 2000rpm.

We drove the 740d in M Sport specification, with optional 20-inch alloy wheels, and yet it rode extremely quietly, and surprisingly comfortably with its adaptive dampers, active anti-roll bars and myriad other tailored driving systems set to Comfort.

Wheels aside, the M Sport upgrade makes no difference to the car’s chassis, but neither extra grip nor added composure is required when you flick over to Sport mode. The steering quickens and loads up slightly, and the dampers tie the car down onto the road very well.

What you end up with is a car that can be driven across country just as quickly as a proper sports saloon – albeit with greater precision than involvement – but with a great deal more comfort, and going a great deal further between pumps than a true sports saloon would.

Should I buy one?

BMW’s diesel engines are the envy of the car industry. It amazed us with the oil-burning motors in the 1996 E36 325tds, the 1998 E39 530d and most recently with the twin-turbocharged units in the 535d and 123d.

It’s got another headline-maker with heater plugs here - a truly remarkable powerplant in a very commendable car indeed.

Jaguar’s new XJ may be hogging the limelight right now, but it’ll have its work cut out winning an Autocar group test with a 740d involved. Because, although this car is expensive, it’s also fast, refined, economical, spacious and quietly brilliant to drive.

Unbeatable? Watch this space.