Sector: Luxury Price: £87,965 Fuel: 100.9mpg CO2: 65g/km

In the quest to produce the most efficient cars, carmakers such as Toyota, BMW and Tesla are increasingly pushing back boundaries. But Mercedes-Benz will make up a lot of ground as it introduces 10 plug-in hybrids between now and 2017.

This is the first, and it will undoubtedly shake up the luxury sector. The S-Class is already the segment pacesetter and this new model, with its eyebrow-raising figures, will certainly prove persuasive, especially for customers making regular trips into central London.

 The drivetrain is a combination of 328bhp biturbo V6 petrol engine and electric motor, which adds the equivalent of another 114bhp – enough to power this 2.2-tonne luxury behemoth to 62mph in a deceptively swift 5.2 seconds (faster than some Porsche Boxster and Cayman variants). Despite this performance pedigree, however, in daily use it is incredibly quiet and, in electric mode, virtually silent, with the barest minimum of road noise intruding into the cabin.

While the refinement is impressive, the economy is even more so. The official fuel consumption is 100.9mpg, with CO2 emissions of 65g/km and an electric-only range of 20 miles (charging takes two to four hours, depending on whether you use a wallbox or a domestic supply). Real-world economy will vary depending how much of its time is spent driving on electricity, but the 51mpg we attained on a route comprising of city streets, motorways and rural highways is still noteworthy.

The biggest question before deciding on this environmental paragon is whether the premium over a diesel engine – in the region of £24,000 – is recoupable. That will be a big hurdle, but the PR kudos, particularly for London-based chauffeur fleets, will undoubtedly prove persuasive. So, while this won’t sell in its thousands, it’s a preview of the technology we’ll see on more affordable models, and is undoubtedly a significant benchmark.