Peugeot 508 e-HDi

In the battle to produce the cleanest compact executive car, this 508 e-HDi joins the BMW 320d EfficientDynamics under the 110g/km barrier. But while the BMW remains as much fun  as less efficient models, the Peugeot’s driving experience is compromised. The gearbox is too ponderous in full auto mode, and slow and jerky if you shift with the paddles. We’d go for the standard 1.6 HDi, or one of the cheaper but smoother petrols.

Can the Peugeot 508 show the competition a clean pair of heels? In recent issues, we’ve driven top-spec GT diesels, in saloon and SW estate bodystyles, as well as the lively 1.6-litre THP petrol. But now, we’re heading to the other end of the range to try the cleanest engine on offer: the 1.6 e-HDi. Fitted with stop-start, it puts out only 109g/km of CO2.

That’s impressive for a large saloon, even though the 508 weighs less than the 407 and 607 it replaces. It’s cleaner than the Passat BlueMotion, although VW is set to launch a 109g/km version later in the year, and comfortably trumps Ford’s most efficient Mondeo. But it doesn’t come without compromise.

Video: watch CarBuyer's video review of the Peugeot 508

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The problem isn’t power: the engine delivers 112bhp, as well as 270Nm of torque. It pulls strongly from low revs and stays quiet and refined unless you’re approaching the red line. 

What’s more, the e-HDi turns in sharply and rides smoothly, even though it features simple MacPherson front suspension, instead of the double-wishbone set-up of GT models. The spanner in the works is the six-speed automated manual gearbox.

It can be used in full auto mode or controlled manually via steering wheel paddles. But however you change ratio, the result is the same: it’s slow and jerky, and you’ll soon get frustrated. Unfortunately, there’s no manual option – this box is needed to achieve the low CO2 figures, and it’s a hefty price to pay.

More impressive is the stop-start system, which uses a reversible alternator instead of a more conventional starter motor. It works quickly, and never failed to fire back up when we lifted our foot off the brake and on to the accelerator in traffic. 

The set-up is also programmed to cut the engine before you’ve come to a complete stop, saving precious drops of fuel without hampering your braking. Peugeot claims it can cut consumption by up to 15 per cent in town.

All this clever fuel-saving tech helps to make this the economy king of the 508 range – and its 64.2mpg combined claim is truly amazing for a family car that’s so spacious and has such a premium feel.

But while the headline figures will appeal to fleet customers (to whom two-thirds of 508s will be sold), for private buyers, this gearbox is a compromise too far. We’d go for a regular 1.6 HDi; it emits 124g/km and offers 30Nm less torque, but is £800 cheaper – and crucially, has a five-speed manual box.