What is it?
This is a diesel-electric hybrid version of the recently launched Mercedes-Benz S-class.
It utilises a 2.1-litre four-cylinder diesel engine and an electric motor, the latter of which is integrated into the car's seven-speed automatic transmission.
This, claims Mercedes, helps the two-tonne luxury saloon to average a staggering 61.4mpg while emitting just 120g/km of CO2. That means the Mercedes will cost you only £30 to tax, although for many buyers that will probably be somewhat of a moot point.
Performance is hardly lacking, with the rear-drive S-class reputed to be capable of 0-62mph in 7.6sec. Its top speed, should you find yourself on a suitable stretch of autobahn, is 149mph.
The hybrid is only offered in one trim, 'L AMG Line', and is priced at £72,260. That means it commands a premium of £1,555 over the conventional V6 diesel in an equivalent specification.
It is, however, £2445 cheaper than the petrol-engined S400 Hybrid – although that particular model is considerably more powerful.
What's it like?
While the S-class impresses on the numbers front, it falls down a little in the real world – primarily because of its four-cylinder diesel engine.
Because the Mercedes has such a refined and composed nature, it comes as somewhat as a surprise when you first hear the diesel engine fire into life.
It's not excessively noisy, even when worked hard, but it lacks the outright mechanical refinement of the six-cylinder diesel offered elsewhere in the range; it's not uncommon to feel a slight vibration through the steering column either.
By no means is it disappointing but it feels at odds with the Mercedes' luxury nature and takes the edge off that 'magic carpet' experience that you might otherwise expect.
The hybrid powertrain does function well, however. The diesel engine cuts in and out quickly and effectively and the electric motor grants the S-class silent low-speed cruising and coasting. The seven-speed transmission is equally competent, shifting through its ratios quietly and unobtrusively.
Charge from the hybrid's battery can be depleted quickly – even when parked, no doubt due to the Mercedes' substantial electrical and ancillary system – but it also replenishes at a sensible rate, meaning there's usually something in store when you need it.
There is, it must also be said, also something immensely satisfying about rolling along in absolute silence in electric mode – a feel-good factor that's enhanced by the fact that the S-class is capable of accelerating in a comparatively swift and eager fashion if needed.
During testing the car returned an indicated 34mpg, which while some way off the claimed average was good given the conditions – and still quite remarkable when considering the S-class' kerb weight.