There’s an electric car revolution going on behind the heavily cloaked development centres of many of the world’s car makers right now – as evidenced by Mercedes-Benz's surprise announcement that a plug-in electric version of its upcoming SLS is already in the works and has been since the outset of its development.

Although not envisaged to go into limited production until 2015, the SLS eDrive is a clear signal of where Mercedes-Benz and its AMG performance car offshoot thinks the motoring world is heading. For while its officials continue to vigorously extol the virtues of petrol and diesel engines – the very ground on which its existing models are based, there is a growing feeling within the German car maker’s engineering ranks that the time for widespread electric and hybrid car usage is not too far off at all.

Read 'Electric Mercedes SLS revealed'

And, by the look at just how advanced its new electric powered gullwing supercar is already, Mercedes-Benz is betting the reach of plug-in electric drive won’t only be restricted to small city cars. Rather, it’ll continue all the way into the top echelons of its line-up. All the way to the top, in fact.