Trends come and go in cars, just as they do in clothes and music. Right now, all the talk is about carbon dioxide emissions, because road tax and company car tax are both now graded on a car’s CO2 output. Car makers are going out of their way to produce low-CO2 cars, and Peugeot’s 508 e-HDI is one of them. 

In the official tests it generates just 109g/km of CO2, a laudable achievement for a well-equipped, family-sized saloon like the 508. That puts it into road tax band B, which means there’s nothing to pay in the first year and just £20 a year after that. Company car drivers pay 15% ‘benefit in kind’ tax. Low CO2 also implies low fuel consumption, suggesting that the 508 e-HDI will be cheap to run. But building a car with the focus on CO2 emissions inevitably means compromising on something else, and in this case the casualty is drivability.

The e-HDI delivers super-low CO2 emissions in two ways. First, it is fitted with a stop/start system which kills the engine when the car comes to a halt, then automatically restarts it when the driver releases the brakes. It’s effective and unobtrusive. But the same can’t be said for the second strategy Peugeot has used to reduce CO2 output: the EGC gearbox.

EGC is an automated manual gearbox – essentially a conventional manual transmission with some clever electronics operating the clutch and shifting the gears so you don’t have to do it manually. An automated manual is more efficient than a true automatic transmission, and it’s lighter and simpler than the twin-clutch transmissions which have gained popularity in recent years. The drawback to EGC as used here is that it is very eager to change up, so minimising fuel economy and emissions but leading to lumpy gearchanges. It’s smoother in sport mode, and better still if you ignore the automatic modes altogether and use the column-mounted gearshift paddles to change gear manually ¬– but that rather defeats the object.

The limitations of the EGC transmission mean many will opt instead for the 508 1.6HDi manual, which has the same engine connected to a conventional manual gearbox and costs around £1000 less. It has slightly less impressive CO2 and fuel consumption figures, but in the real world the differences are likely to be negligible – and it will be more satisfying to drive.