By cutting out the engine when the accelerator pedal is lifted, the pounds 11,495 Golf Ecomatic reduces emissions by an average of 25 per cent compared with a standard diesel car.
If every driver in London traded in their current vehicle for an Ecomatic, the capital's fuel consumption would be cut by half, according to government pollution experts, Warren Spring Laboratory.
Working on the premise that when the engine is not running, it isn't polluting, the Golf's power source is typically turned off for 60 per cent of a drive through the city. The engine cuts out automatically after a second whenever the accelerator is lifted. Power returns rapidly when the accelerator is pressed.
The 1.9 litre diesel gives an urban fuel consumption of 61 miles per gallon. Carbon monoxide emissions fall by 36 per cent and nitrogen dioxide emissions by 25 per cent.
Impressive as these figures are, if the car is to succeed Volkswagen has the difficult task of persuading motorists to get accustomed to a new way of driving.
Even the cabin is different - there are warning lights to tell you when to change gear, and a button on the end of the wiper stalk to engage permanent engine braking.
There's no clutch - gear changes are made by lifting the accelerator and moving the gear lever. This is an advantage for urban motoring where constant use of the clutch can be tiring, although this is already the case with automatics.
On the downside, the cut-out system means that the car is fairly lethargic from standing situations. London drivers who like to dart in and out of traffic, and who need immediate power to overtake and move quickly away from traffic lights, may be disappointed.
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