The major details of the VW XL1, the German manufacturer's all-composite, 795kg, super-aerodynamic (Cd 0.189), two-door hybrid have been on the record for months.

It is a monocoque car, close enough to production for a run of 250 to have been announced, powered both by a two-cylinder, mid-mounted 800cc diesel engine producing 50bhp and an electric motor that adds another 27bhp.

The pair drive through a seamless seven-speed dual-clutch gearbox. Actually, the total clutch count is three – two in the gearbox and another between the engine and motor – to allow the car sometimes to be driven on electric power alone.

The XL1’s efficiency is already legendary: in windless conditions it needs just 8bhp to maintain a steady 62mph and it can return up to 313mpg. And yet if you were to deploy all available power it would hit 125mph, although for now it’s governed at 100mph.

From a standing start the VW will reach 62mph acceleration in a respectable 12.7sec; indeed, as soon as we start our drive, it becomes clear that the XL1 delivers normal-to-brisk performance.

The XL1’s all-up weight of 795kg is impressive, but its aerodynamics are even more staggering. Thanks in part to a frontal area barely two-thirds that of a Polo, its drag factor is half that of equivalent cars.

However, airflow management involves more than sleekness. In the XL1’s case, engine bay cooling air is collected from a high-pressure area within the rear diffuser and ducted past the engine, exhausting through two ‘nostrils’ on the car’s upper surface.

Most of the time, the flow is enough to keep things cool, but there is an assistance fan (reminiscent of the fan visible in old Beetles) to augment flow on really hot days. 

Our mission is a practical one: to explore inner London by XL1. VW has decided to make a feature of the car at both the Coronation Festival and Goodwood Festival of Speed and, given such exposure, the car had better work properly.

Mind you, VW’s version of practicality doesn’t yet extend to putting a price on it: the beancounters won’t reveal all until Frankfurt show time in September.

Speculation has it that early adopters would pay around £86,000, though VW bosses say they’d rather see the car “priced to be used”. The XL1 is an emblem of VW’s technical prowess and they want it driving around.

Once you’ve settled into the Volkswagen XL1’s perfectly shaped bucket seat (a space-saving carbon fibre moulding) and pulled down its large gullwing door, what strikes you about this revolutionary car’s instruments and controls is how normal they seem.

The instruments, info screen and gearchange are as classy and familiar from production VWs as my view of London’s streets through the steeply raked windscreen, bounded each side by surprisingly thin, bare metal A-pillars.

When I remark on them, my passenger, a Belgian engineer called Steven, tells me VW resisted trimming the pillars because it would have added 3mm to their thickness, when thinness is the target. 

Press the start button and there’s no sound unless the 5.5kWh lithium ion battery (under the passenger’s feet) needs charging, which it usually doesn’t. You see a ‘Ready’ notice on the dash, select D and squeeze the accelerator.

The car moves willingly away and picks up speed easily, advertising its light weight. Once rolling it maintains speed remarkably well because there’s very little aero drag, plus there’s a built-in freewheel.

We drive for an hour around inner London (Westminster Bridge, Parliament Square, The Mall, Lambeth Bridge) and I estimate that the balance-shafted diesel engine – which emits a machine-gun rattle but seems not to vibrate at all – is only running for about a third of the time.

The steering is unassisted (a big weight saving) because the wheels and tyres are skinny, but the car is easy to manoeuvre once you get used to the way rim effort builds in corners. In every way, the XL1 is a neat and easy handler.

Given a relative lack of suspension travel because the car is so low, it also absorbs road irregularities well, although you have to watch London’s ruts and speed bumps.

I’m convinced this is a car I could drive every day. In fact, I’d like the men from VW to download my fuel consumption because I reckon I’ve hit 200mpg without really trying.

Volkswagen XL1

Price TBA; 0-62mph 12.7sec; Top speed 100mph (limited); Fuel economy 313mpg (combined); CO2 21g/km; Kerb weight 795kg; Engine 2 cyls, 800cc, turbodiesel plus electric motor; Installation Transverse, mid, RWD;  Power 67bhp; Torque 103lb ft; Gearbox 7-spd dual-clutch auto

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