Although you can still specify BMW's 7 Series flagship saloon with a punchy six-cylinder diesel or a petrol V8, the vast majority of these super limos now come with secondary filler flaps. 

Whether captains of industry know, or care about which power source is wafting them between high-pressure engagements, the guys tasked with the crack of dawn airport runs and the company accountants know only too well that the 745e plug-in-hybrid is the savvy choice.

While a stretched wheelbase 740d diesel still makes plenty of long-distance sense, thanks to its low 40s mpg and more affordable P11D - on average, it's £7,000 less than a 745e - and the diesel boasts an additional 95-litres of boot space, these numbers are ultimately compromised by a 174g/km CO2 output, which brings with it a top-notch 37% BIK implication. By contrast, a similar spec long-wheelbase 745e emits just 52g/km, meaning bills are levied at a far more palatable 15%. 

Putting the cost differentials to one side, where the 545e really scores, and crucially so in this rarefied class, is its vastly superior refinement. 

For starters, with an electric-powered range of 29 miles and providing you have reasonable access to the charging network, chances are the 3.0L, turbocharged, six-cylinder petrol engine will lie dormant, if most of your engagements lie within city postcodes. When the straight-six engine does chime into life there are none of the combustion rattles associated with diesel power, just a faint mechanical hum. This smooth integration and inherent silky refinement are complemented by slick, self-centering steering and precision calibrated accelerator and brake pedals, ensuring every traffic light encounter starts and finishes with a seamless take up or graceful retardation. 

It's just a shame the same cannot be said of the ride quality. Although four-corner air suspension and adaptive damping are employed to provide cosseting body movements, which left untainted convey a real sense of sublime isolation, this serenity is too often interrupted by more abrupt impacts, which tend to transmit quite a bit of jitter up through the Axminister. 

More encouragingly, wind and road noise are wonderfully masked, thanks to layers of acoustic glass on the side windows and rear screen and hefty sound deadening around the rear seat area. 

Obviously, the 7's primary reason for existence is to provide extensive rear legroom so its rear passengers can stretch out after a hard day counting their money. However, to provide the ultimate slouchy experience, BMW offers an optional rear seat comfort package, which adds extensive electric seat adjustment, powered sun blinds and brogue cosseting footstools. You can also reduce the tedium of longer journeys by speccing the rear entertainment package, with a pair of screens to stream movies or configured to operate as eye-level laptop screens.

As well as surroundings decked out in oceans of finely tailored leathers and burnished aluminium highlights, the 7's bespoke seats elevate comfort to Slumberland levels, while sensory delights for the driver include silky weighted switchgear and a super rapid infotainment system. Other than the encyclopedic extent of its menus there's nothing particularly unique about the 7's i-Drive system, as most of its constituents are found in lesser BMWs. The essential usability of the system is so well thought through though,
that it is able to provide access to a mind-boggling variety of options, either via rotary dial, touchscreen, gesture control or voice activation, all without confusing the operator.