One of the most fascinating experiences I have had recently was a two-day technical mega-brief on BMW’s upcoming Megacity Vehicle.

However, even though the first MCVs will be pure electric cars, it will be the ‘range-extender’ version (probably powered by a 1-litre, two-cylinder, engine/generator) that will be the real ground breaking model.I have become convinced that the future for ultra-low CO2 vehicles, especially for anything bigger than a Golf, lies with range-extender technology.

One of the biggest problems for pure-electric vehicles is not just the driver’s ‘range anxiety’ but also the huge draw on battery power required by lights and heating in winter. Cold weather also wallops the battery’s performance.

Using a range-extender layout fixes these problems and should be no more expensive than a pure electric car.

The key about combining a petrol engine/generator and battery pack is that it can deliver the performance of a big internal combustion engine along with very low emissions of both CO2 and pollutants.

Take Jaguar’s Limo Green project. It’s driven by an electric motor good for 195bhp and 295lb ft of torque. With all the torque available from start-up, performance is first-rate.

Ultimately, however, the electric motor is powered by a combination of a tiny, three cylinder, 47bhp, Lotus petrol engine/generator and a relatively small 8.6kW battery.

Normally, the full potential of a conventional big engine is only needed when accelerating; the rest of the time it’s partly a dead weight.

Using the XJ’s battery pack as kind of power store, topped up constantly by the engine/generator, and taking advantage of the electric motor’s huge torque, means that the XJ Limo Green can deliver real-world pace at no more than 130g/km and less if the car’s battery is charged overnight from the mains.

A 1.2-litre, 130g/km, 295lb ft Jaguar XJ seems like science fiction. But it’s not. It’s entirely real and not very far from production. There are other clear advantages, too. The drivetrain is smoother, quieter, much less complex, longer lasting and cheaper to service.

Britain, for once, seems well placed in the technological race, with Jaguar’s Limo Green tech also likely to be adopted by Land Rover. We could also see the Vauxhall Ampera/Chevy Volt range-extender built in the UK.

The Northern Irish-built (and Autocar-inspired) New London bus project will carry nearly 80 passengers with a 2.5-litre range-extender transmission. A conventional double-decker uses an 8-litre turbodiesel motor, which is far less economical and far more polluting.

Here’s my prediction. Ten years from now, the Mk5, all-aluminium, Range Rover will weigh 1900kg, be powered by a 1.3-litre petrol engine/generator and compact battery pack. It will be good for 135g/km and the air coming out of the exhaust will have lower pollutant levels than the air going into the engine.

Try calling that a gas-guzzler.