Whole life cost calculations showing the effects of never charging plug-in hybrid vehicles (PHEVs) have been published by Fleet Logistics UK and Ireland.

The fleet management company says that PHEVs can be an ideal option for company drivers looking to transition between conventional petrol and diesel cars and electric cars, provided they are used properly.

The fleet industry has recently been awash with warnings of drivers choosing PHEVs for cheaper tax rates, but then never plugging them in to charge the battery and running them solely on the petrol or diesel engine.

Looking at published figures for one petrol PHEV saloon, Fleet Logistics found that fuel consumption driving on the petrol engine alone dropped from an official 176.6mpg to just 50.4mpg, meaning a monthly fuel cost increase of more than £57 on a 10,000 mile per year contract.

This would increase to £86 per month on a 15,000 mile contract, £115 per month on a 20,000 mile contract, and £145 per month on a 25,000 mile contract.

According to Fleet Logistics, this has a marked impact on the car’s whole life costs, which would increase by £46.84 per month on a 10,000 mile contract, and by £142.40 per month on a 25,000 mile contract.

Fleet Logistics country head Sue Branston said: “We believe PHEVs have a role to play in helping companies transition between internal combustion engines and electric vehicles. However, it is important they are used correctly so as not to impact air pollution as well as cost.

“They do not suffer from range anxiety and therefore can be suitable for even long-distance fleets. However, if they are not recharged regularly and in line with manufacturer guidance, then they become more costly to operate for the business than initially forecast.

“At the same time, drivers do not get penalised for not charging their vehicle because the BIK tax scales don’t recognise the difference between driving on electric or driving on petrol. Companies may want to consider some policy amendments for those drivers who are not charging their PHEVs correctly which can easily be measured by the additional fuel costs they are incurring.”

Branston said that PHEVs could play a role within an optimum fleet policy along with RDE2-compliant diesels and petrol models for medium to long distance drivers, and none should be ruled out without proper analysis.

She said: “PHEVs, when driven correctly, are a step forward in helping fleets tackle air pollution and decarbonising their transport. However, driver habits must be monitored to realise both the financial and environmental benefits.

“RDE2 diesels not only give the range and fuel consumption that many fleets still need for their longer distance drivers, but they also have the advantage of avoiding the 4% diesel surcharge and from this April may attract a 2% reduction in BIK rate.

“Many petrol variants are not far behind diesel in terms of mpg and should therefore not be ruled out. So, we are continuing to advise our clients that diesels and petrols, like PHEVs, can have a role to play in defining the optimum fleet policy in the medium term.”