It’s when it comes to PHEVs that the world becomes a great deal more complicated. Just to remind you, PHEVs are hybrid vehicles with a battery large enough to power the car on its own for a significant distance.

Flawed official economy tests

We have already written about the deeply flawed economy tests for these cars which takes a factor of the CO2 emissions from two impossible situations, with the battery completely full and it completely empty. This results in absurdly high, three-figure fuel economy claims and equally fanciful boasts of sub-50g/km CO2 emissions.

It’s hardly surprising therefore, that in real-world use a PHEV consumes more fuel than the brochure claims. Last year Which? published a report claiming that on average PHEVs are 61 per cent less fuel efficient than their manufacturers claim. Another report from Transport Analytics using tests from Emissions Analytics showed that in real-world tests, PHEV emissions were 28-89 per cent higher than claimed. In conclusion it suggests that Europe could be heading into a “new dieselgate”.  

Few believe PHEV economy tests to be anything but pie in the sky, although it’s hard to blame car makers for claiming the figures that result from a mandated test. Indeed, if you charged your PHEV frequently and never travelled more than its electric range so the engine never actually started, the effective fuel consumption would be zero. 

But quite apart from the unlikely possibility of this happening, we need to know each PHEV’s actual battery-only range.

What’s the real electric range?

An obvious way of testing this is to simply drive a vehicle with a full battery on the WLTP test cycle until the engine starts, but not all PHEVs work like this. Some continuously blend the power of the electric motor and the battery according to demand so it’s well-nigh impossible to perform this sort of battery-only test. 

For this reason, and to set a level playing field for comparison, there’s a test of all PHEVs which includes an efficiency portion, defined as the portion of the total charge-depleting range attributable to the use of electricity from the battery over the course of the test.

It’s called the Equivalent All Electric Range (EAER), but what happens when you apply this test to a range of PHEV vehicles? Perhaps unsurprisingly, the electric range goes up.

Take the new Vauxhall Astra Hybrid-e, for example. The brochure claims an All Electric Range (AER) of 37 miles, but an Equivalent All Electric Range (EAER) of 43 miles.

Is HMRC using the wrong test data to calculate BIK?

That would be all very well and just another example of how PHEVs have flummoxed the legislators, but for one fact, which is the HMRC’s acceptance of these EAER figures in the calculation of benefit in kind.

So, for this year and next, instead of paying 12 per cent BIK, which is where the lower and more realistic EAR figure would place it, company drivers of the Astra hybrid will find their BIK calculated on only eight per cent thanks to the enhanced but highly unrealistic EAER figure, which moves it into the next band.