From the 'ultimate driving machine' through 'efficient dynamics' to 'the power of action', BMW's marketing message may have subtly altered over the decades, but what hasn't changed is its unstinting devotion to the 3.0-litre straight six-cylinder engine. 

Yes, this legendary engine has been the subject of plenty re-engineering since its inception almost five decades ago, and yes it has been significantly boosted, through advancements such as high-pressure fuel injection, turbocharging and more latterly hybrid electric drive, but the characteristic virtues of scintillating power delivery and silky refinement remain the key ingredients that make BMW's jewel in the crown engine so iconic. 

For how much longer this status will persist is difficult to say, given the gathering pace of an increasingly fully electric BMW line-up, but for now this is a power source that still deserves to be cherished and enjoyed, especially when sitting under the bonnet of a 545e X-Drive M Sport.

Not to be confused with the 530e, which despite the badging actually employs a turbocharged four-cylinder engine, the 545e with its amalgamation of a half dozen in-line cylinders allied to a potent electric motor ensures it is also capable of delivering deathly hushed progress for up to 31-miles on electric power alone. Add in a silky eight-speed automatic gearbox, and regardless of which driving source you are employing, progress is all but seamless. Thanks to a standard four-wheel drive X-drive layout, despite the near 400bhp power output, traction and grip are incredibly sure-footed, while cornering control is reassuring predictable and engagingly adjustable. 

This said, the 545 is not entirely flawless. As with all 5 Series, a certain amount of impact shake invades the cabin when colliding with sharper impacts or grainier road surface imperfections. Chances are you'll be largely unfazed by this underlying trauma but if you are inclined to drive or sit in the front passenger seat with your noggin resting against the head restraint, then the level of disturbance radiating through the seat backs can be very
telling indeed.

Of course you may be too smitten with your surroundings to pay much heed to this aspect, as the 545's cabin is such a paragon of fine taste and understated elegance. What's more, given the amount of sustainable/cheaper interior materials being used in many fully electric vehicles, it's arguable that in years to come the 5 Series will be fondly remembered as a high-water mark in executive class cabin appointment. 

Complete with sharply focussed displays and finished throughout with luxurious materials, lit with subtle, ambient lighting, every switch, dial and lever has a precise haptic feel conveying an overriding sense of precision engineering.

Although the latest generation of electric BMWs employ more expansive panoramic screens, the 545's 12.3in infotainment display is not to be sniffed at and a similar sentiment can be levelled at the optional head-up display, which is possibly the most easily scrutinised version of its type. Throw in an i-Drive operating system that produces broadband fibre clarity and responses times, while also permitting access to emails, calendar entries and contact details, then it's difficult to think of a more rounded office on wheels than the 545e. 

Along with the hefty price premium and the slightly compromised ride quality, there are a couple of other drawbacks to consider. Firstly, you need to have somewhere to plug your 545e in, because if you don't, those impressive mpg figures will become the stuff of Hansel and Gretel. Then there's the 120-litre sacrifice in boot space and 22-litres loss in fuel tank capacity compared with a 520d, due to the location of the hybrid battery pack.