It's official. Volkswagen is going to build the ridiculously fuel-efficient, 21g/km CO2 emissions, 100mpg+ XL1 diesel-electric hybrid. And you're going to be able to buy it.

The news comes as the 2013 Geneva Motor show gets into full swing.

We've seen concept versions of the VW XL1 before, of course. But the Geneva show has brought us the final production version. The one you'll be able to buy.

So what's the XL1 actually like? First up, it's strictly a two seater. The body work is high-tech carbon fibre, stands just 1.15m tall and weighs a mere 795kg.

To put that into context, that's a good foot lower and half a tonne lighter than a standard family hatchback.

XL1

Combustion power comes from a tiny, 800cc two-cylinder diesel engine, good for just 27bhp.

Add to that an electric motor and a 5.5kWh battery pack, stir in that low kerb weight and an ultra aero-efficient body and you have some surprisingly decent performance numbers.

Crazily low carbon

The XL1 will do very nearly 100mph and hit 60 in 12.7 seconds. Much more dramatic, of course, are the CO2 emissions of just 21g/km and 127mpg fuel efficiency.

XL1

It's only fairly recently that the first sub-100g/km cars went on sale, so a car with emissions measuring just one fifth of that is quite spectacular

Other highlights, include techy ceramic disc brakes, a seven speed dual-clutch gearbox and light-weight aluminium crash structures. Even the dashboard is made of a light-weight wood-based fibre.

There's no word on pricing, but with all that cutting edge technology, it won't be cheap.

XL1