You may already be familiar with the 2017 BMW 5 Series. It starred in that horribly irritating pop-up ad that until recently shot sideways across every webpage you summoned. That alone would have been enough to make me buy Mercedes-Benz. But let’s be generous at the outset. Whatever the numbers and letters on the back of the variants – 520, 530, 540 or 550; d, e or i – the 5 is a serious executive saloon for serious executives and guarantees quality, comfort and luxury. It is more agile than of old, quicker, lighter and more efficient. And so it had to be, with the Jaguar XF, Audi A6, Lexus IS and Mercedes E-Class all ganging up to boot the 5 Series back to Bavaria. Slightly longer and wider than its predecessor, this is the seventh generation of a model that in 45 years has never gone out of fashion. It disguises its muscle by being sleek and svelte, with a low-slung aspect reflected in the driving position. Its curves captivate, its bodylines invite you to linger and its LED headlights and twin-kidney grille combination means it smiles like a shark. The 520d comes in a basic iteration and as the US$599,000 Sport Line, which we tested. Ours was powered by a two-litre, four-cylinder engine producing 190hp and 400Nm torque at 1,750rpm. That might not sound too intimidating, but thanks to what BMW calls its TwinPower Turbo it feels like more than enough to keep the motorway speed cameras in a job. Unless you prefer to view cars lying on your back, staring upwards from a concrete pit, you might not realise the 5 Series’ fundamental design and engineering platform is shared by the big, posh 7 Series. But whereas a magnificent 7 budget buys a swanky carbon fibre-rich chassis, the new 5 packs in a lot of aluminium – not that that’s such a bad thing when it translates into a saving of about 100kg on its forebear. More aerodynamic than a Tesla Model S and sitting pretty on 18-inch light alloys, the rear-wheel drive Sport Line maintains the perfect balance of an Olympic gymnast, no matter how heavy your right foot or how cunning the corners on sinuous roads. Its eight-speed Steptronic automatic transmission might recall something from an ’80s aerobics class, but its moves are smooth whatever driving style you select. Choose Sport mode for the most fun: nudge the stumpy stick into manual and shifting via the paddles is rapid and just as precise as gear changes in fully automatic. The 520d will hit 100km/h from zero in a respectable 7.5 seconds and progress to a top speed of 235km/h. BMW has also installed something it calls Syntak, or Synergy Thermoacoustic Capsule technology, which in English means its soundproofing reduces engine noise (considerable at kerbside) to allow a hushed ride inside. The five-adult cabin is generously proportioned, as is the 530-litre boot, which expands with the help of the 40:20:40 rear-seat splits. Up ahead, driver and companion sit in snug sportiness, although regrettably much of the comfort front and back comes at the expense of flesh and bone. Tesla, with its sumptuous leatherette pews, has proved there’s no excuse for slaughtering animals to pad out the insides of vehicles. Electronic entertainment and safety goodies jostle for attention in the 520d; among the latter are computer warnings guarding against pedestrians, hostile vehicles, lane changes, sharp bends and more. Cameras predictably make parking a cinch and the Driving Assistant Plus programme allows you to relax in traffic jams or on long motorway jaunts while the car takes over. Such a litany of new-fangled devices is all well and good, but in the long run how many driving skills will be lost? So there we have it: an outstanding saloon sure to post excellent sales figures in a competitive market. But then we come to that tell-tale initial, “d”: d is for dirty; d is for diesel. Industry gossip has it that the 520d will be the 5 Series’ best-seller, which, when you consider the following, reveals much about car manufacturers and buyers. Increased fuel efficiency, reliability and rugged build quality mean diesel engines generally outlast their petrol driven equivalents and deliver greater value for money. Diesel cars are also faster from a standing start than most petrol-powered rivals. Diesel engines in cars, according to European figures quoted by The Guardian , can produce nitrogen oxides at 10 times the level of buses and heavy trucks, which are more stringently tested. From July 1, the implementation in Hong Kong of tougher emissions standards for cars may help dilute the noxious, death-dealing pollution soup that flows through the city. Nevertheless, and whatever technological advances in cutting toxicity car companies may claim they are making, trying to justify diesel-car production at a time when many have seen the electric-car light looks like a lethal paradox. Perhaps, when buying a car, you should let your conscience be your guide – as Marvin Gaye and Jiminy Cricket sang.