Drivers misusing plug-in hybrid vehicles (PHEVs) by not charging them could be increasing the monthly whole-life cost by more than £140 a month.

That’s according to new figures from Fleet Logistics UK, which says that PHEVs provide an ideal business tool for fleets looking to transition between conventional ICE (Internal Combustion Engine) engines and electric vehicles – provided they are used properly.

Analysis by the firm based on the example of a BMW3 Series 330e automatic saloon and figures from ongoing work with clients, found that fuel consumption drops from the official 176.60mpg to 50.40mpg if driven on the petrol engine alone. As a result, the monthly fuel costs increase by more than £57 on a 10,000 mile per annum contract.

The fuel cost differential is even more marked over longer mileage intervals. For example, on a 15,000 mile per annum contract the fuel cost goes up by £86 per month, on 20,000 miles per annum it increases by £115 per month, and on 25,000 miles the fuel cost rises £145 per month.

This has a marked impact on the car’s whole-life costs, as per the chart below. As an example, on a 10,000-mile contract, the whole-life costs of the BMW PHEV increase by £46.84 per month*, while on a 25,000-mile contact, they rise by £142.40 per month, if only the petrol engine is used – and for a large fleet running several hundred of these cars, the cost increases are clearly substantial.

Fleet Logistics UK’s figures underscore latest research from Emissions Analytics that shows the poor real-world results of PHEVs when not plugged in. Of all PHEVs tested by Emissions Analytics, which includes petrol and diesel versions, the average performance used in this way is 37.2mpg (7.6 l/100km) and CO2 emissions of 193.3g/km, which is 62.5% worse than the official NEDC results.

There has been high-profile concern over driver misuse of PHEVs within the fleet industry in the last few years. According to ACFO, there have been widespread reports of fleets returning their cars early to leasing firms due to significantly higher-than-expected fuel consumption; the organisation has for some time been calling for Advisory Fuel Rates (AFRs) for all PHEVs to clamp down on this.

More recently, TMC has warned that its real-world mpg data has revealed many PHEVs actually cost more in fuel pence-per-mile than typical diesel or petrol company cars due to drivers not charging them

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

“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,“ she said.

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

“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,” she said.

**Costs of fuel applied are 129.20p per litre (petrol) and WLC calculations assume 19% Corporation Tax rate, 100% VAT recovery and include RFL, servicing, maintenance and breakdown cover.