Why ‘green’ plug-in hybrids are actually the highest-polluting vehicles in UK fleets

18th October 2017

Plug-in hybrid electric vehicles (PHEVs) have become a common fixture in the automotive landscape. More than 62,000 of them have been sold in the UK since 2012 and demand seems to be on the up.

That’s due to their ability to offer all-electric, zero-emission motoring without the worries linked to limited mile range or the necessity to regularly find a charging station.

Plug-in hybrids seemingly provide the best of both worlds. They take a conventional petrol or diesel engine and pair it with an electric motor and a lithium-ion battery, which means it can drive for more than 30 miles using just electric power.

It only turns to the petrol or diesel when the battery runs dry or if the driver gets heavy with the right-foot and demands a higher performance.

When used forgivingly and in the correct manner, plug-in hybrids can return phenomenal fuel economy figures – well into triple figures in most cases – while CO2 emissions are tiny, shrinking to the teens for some models.


The result should be a three-way win. Company car drivers enjoy a low benefit-in-kind (BIK), organisations reap the benefits of decreased fuel costs and a greener corporate image, and the environment is thankful for the less polluted air quality.

Notice how we said ‘should’ though?

That’s because evidence has emerged that in many cases, plug-in vehicles aren’t being used in the most effective manner and are very often being ran as regular petrol and diesel cars, neglecting the myriad advantages they’re frequently hailed for.

Real-world data from The Miles Consultancy (TMC) shows that PHEVs are actually the highest-polluting company cars in terms of greenhouse gas emissions.

TMC’s figures, obtained using its Mileage Capture and Audit system, took into account seven models of PHEV covering 12 different carmakers.

Average CO2 output of PHEVs in day-to-day use was clocked at 168g/km, much higher than the 13g/km promised by the BMW i3 Range Extender and the Mitsubishi Outlander PHEV’s 41g/km.

Mpg barely a third

Fuel economy fell short too, averaging at 45mpg, barely a third of the 130mpg commonly advertised.

With plug-in hybrids using three-times more fuel during actual use than official figures would suggest, TMC went as far as labelling PHEVs as ‘fake low-emission vehicles’.

Additionally, PHEVs in TMC’s sample emitted more CO2 in real-world driving than regular diesel company cars, it was found (168g/km to 158g/km – PHEV to diesel).

Overall, this shortfall in the cars’ actual efficiency is vastly over-inflating the proposed benefits pushed by PHEV manufacturers. While drivers of Mitsubishi’s Outlander PHEV enjoyed a BIK figure of nine per cent, it should really be around 33 per cent for those using it as a pure petrol car.

Opposite effect

There is also the real risk that fleet managers are using PHEVs with the right intentions, but unknowingly increasing their fuel bills.

Molly Benton, brand manager at Fuel Card Services, comments: “The only person really benefitting out of PHEV misuse is the driver, who is paying lower BIK.

“Any tax benefits in place for PHEVs may only be short lived because after 2019, only fully-electric vehicles will receive sizeable tax breaks.”

She added that with hybrids losing their special tax status and conventional vehicles facing increased air quality penalties, it will become more difficult for fleet users to identify cars that provide the right balance of running costs, range, taxation and emissions.

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