SECTOR Upper Medium  PRICE £31,450  FUEL 78.5mpg  CO2 95g/km

While Citroën has debuted PSA’s Hybrid4 diesel-electric drivetrain as a high performance, four-wheel drive option for the executive class DS5, Peugeot’s approach has been to highlight the technology’s off-road abilities with the 3008 crossover and Audi Allroad-esque 508 RXH.

The 508 HYbrid4 breaks that mould. It uses the same 161bhp diesel engine and 36bhp electric rear axle as the RXH, but without the chunky bodywork cladding and raised ride height of its closest relation. The emphasis is on making this the most efficient 508, and with one of the highest power outputs, too.

A combination of 95g/km CO2, four-wheel drive and high efficiency makes this difficult to match in the D-segment and an attractive fleet option, helped by the 3% BiK surcharge for diesel hybrids being removed earlier this year. But it’s a shame that it couldn’t have withheld just one more gram of CO2, as this would’ve kept it in the second lowest banding when the BiK changes announced in the budget come into effect in 2016.

Hybrid4 is a clever drivetrain, and neatly packaged into the 508 saloon. The motor and battery are hidden under the boot floor, and the only visual clue is a discreet grille badge. Interior changes are as subtle, with a hybrid display in the instrument binnacle and navigation screen and a power gauge which replaces the rev counter.

The only downside to the packaging is the boot becomes very shallow as a result.

Drivers carrying deep boxes, for example, will have to put them on the back seat instead.

UK buyers will get a single trim level, based on the 508 Allure. It’s well-equipped, with keyless entry and start, electrically adjustable heated leather front seats and an intuitive infotainment system with satellite navigation and Bluetooth.

There’s little to get used to. The car starts in its most efficient Auto mode, which uses diesel and electric power to return the most miserly fuel efficiency available, and it drives like a conventional automatic car with an overactive Start/Stop system. Economy can be boosted further by switching to ZEV pure electric mode at low speeds depending on battery charge, ideal for clawing back extra range at roundabouts.

The remaining 4WD and Power modes combine both power sources for an electric ”boost” function or to provide extra grip as required. Those familiar with PSA’s ponderous electronically-operated manual will be glad to hear it’s much better here, with the electric motor cutting in to smooth the gaps between gear changes.

But, with an additional 140kg on board it’s not fast even with the extra power.

Performance is brisk, but this is outpaced by the lesser-powered non-hybrid diesel. And that’s not its biggest problem.

At motorway speeds, the motor and battery are dead weight. There’s no ability to decouple the engine, as some hybrids can, at high speeds to ”sail” on electric power and this hurts economy. Drivers expecting close to the claimed 78.5mpg could feel short-changed at the more realistic mid 50s to the gallon offered on long distance trips – not worlds apart from the 2.0 HDI 163.

There’s a knack to finding the best efficiency. Drive in ZEV mode as often as possible, use AWD to let the electric motor assist the diesel engine at high speeds and gentle driving will give an uplift in economy. There are plentiful rivals on the way, so it’ll be interesting to see what Peugeot introduces in a mid-life refresh to make the system more valuable for motorway drivers.

Verdict

The 508 Hybrid4 saloon may struggle to achieve its on-paper efficiency figures, but it offers gutsy performance and grip for the UK’s unpredictable winters without being a big polluter or expensive to tax. Drivers regularly using long stretches of motorway may find the 2.0 HDI 163 a more suitable option.