Plug-in hybrids emit far more than official tests claim, new Transport & Environment analysis finds

What the new analysis claims

Clean transport campaign group Transport & Environment has published analysis saying the gap between official plug-in hybrid fuel economy figures and real-world efficiency is roughly six times wider than advertised. According to the group's findings, real-world PHEV emissions are only about 14 per cent lower than conventional petrol and hybrid cars, while official test claims put the reduction at 83 per cent — a 69 percentage-point discrepancy. This is Money reported the figures, with the publication noting the campaign group's argument that official emissions figures are misleading for buyers. ²

The Energy Mix's report on the same body of work gives slightly different figures, stating that official estimates assume PHEV emissions among European drivers should be about 75 per cent lower than fossil-fuel equivalents, while T&E finds they are actually only 19 per cent lower on average. The two reports describe the same core finding — that official assumptions overstate how much driving is done on electricity — but preserve different numbers, so both are presented here as reported rather than reconciled. ¹²

T&E attributes the gap mostly to what it calls flawed assumptions about how much driving is done in electric mode. The group's analysis shows PHEVs are driven on the electric motor 41 per cent of the time on average, including combined mode where the combustion engine is also working, and only 27 per cent of driving distance is done with purely electric driving. The Energy Mix reports T&E's conclusion that emissions from PHEVs can be as much as five times higher than expected as a result. ¹

Lucien Mathieu, cars director at T&E, said in comments reported by This is Money: 'A decade after Dieselgate, it is outrageous that Europe is once again debating whether to keep using misleading emissions to sell cars.' He added that drivers 'deserve the truth, not another fix that shields carmaker profits while leaving motorists hundreds of pounds out of pocket.' These are the campaign group's statements, reported by the publication, not independent findings. ²

Why the official figures diverge

The discrepancy centres on the utility factor, the metric used in official fuel economy lab tests to estimate what share of driving a PHEV completes on battery power. According to The Energy Mix's report, official projections have assumed that a PHEV with a 70-kilometre electric range would drive about 80 per cent of the time in electric mode. T&E says in practice many drivers do not charge often enough to maximise electric distance, and that PHEV electric motors are comparatively weak at higher speeds, with the combustion engine able to kick in if drivers accelerate hard even when battery charge would otherwise keep the vehicle electric. ¹

Survey-based research from chargepoint manufacturer CTEK, cited by This is Money, underlines the charging-habit issue: one in six PHEV drivers never plug in, and another 10 per cent charge only once a month. Overall, 39 per cent plug in daily, 27 per cent twice a week and 9 per cent weekly. This is Money reports that this lack of charging underpins the 69 percentage-point discrepancy T&E identifies. ²

The findings align with earlier work by the Energy and Climate Intelligence Unit, which This is Money reports warned earlier in 2026 that PHEV drivers could be spending almost double expected fuel costs, because petrol costs more per mile than electricity and many drivers do not charge frequently enough. The ECIU research, as reported, found PHEVs consume 490 per cent more fuel than claimed. ²

Cost implications for owners

This is Money reports that PHEV drivers could be paying more than £570 a year extra in fuel compared with what manufacturers claim, based on T&E's analysis. The publication's own earlier reporting, cited in the article, estimated average annual fuel and electricity costs for top-selling UK plug-in hybrids at around £540, but with the ECIU finding of 490 per cent higher fuel consumption than claimed, the true annual bill averages £1,030. These are UK-market estimates and UK fuel-price conditions, not Australian figures. ²

The publication also tallies broader ownership costs: when servicing, tax, insurance and higher purchase prices are factored in, a new PHEV costs £4,150 more on average than a comparable electric vehicle in the UK, according to This is Money's summary of the analysis. It notes fuel prices have been rising amid tensions between the US and Iran, increasing the additional cost to drivers. These conditions and prices are specific to the UK market and reporting. ²

Demand context matters to the finding's significance. This is Money reports UK PHEV registrations jumped 55.5 per cent year-on-year in September, and attributes part of the model class's growing availability to cheaper new entrants from Chinese brands. The Energy Mix notes governments have relied on PHEV emissions reductions to make short-term regulatory targets appear more attainable while EV manufacturing capacity and charging infrastructure remain constrained. ¹²

Regulators respond — and political resistance

The EU is moving to close the gap by recalibrating the utility factor used in official ratings, using real-world fuel consumption data transmitted from on-board fuel consumption monitors installed on new vehicles since 2021, This is Money reports. The Energy Mix details the correction schedule: the assumed share of driving done in electric mode for a 70-kilometre-range PHEV is set to fall from 80 per cent to 54 per cent for 2025/26 projections and to 34 per cent for 2027/28. ¹²

There are knock-on effects for vehicle design. T&E notes, as reported by This is Money, that the initial adjustments planned for 2025-26 have already pushed automakers to fit larger batteries and extend electric range. According to the European Environment Agency, cited in the same report, these longer ranges offset three-quarters of the official CO2 increases triggered by the rule changes, with future advances potentially keeping emissions below 50g of CO2/km. ²

The recalibration is not settled politically. This is Money reports that as a key November update to PHEV accounting rules approaches, Germany is lobbying to freeze further utility factor adjustments during Franco-German negotiations on a broader automotive package. T&E characterises the choice facing the European Parliament and Council as between protecting drivers' wallets and allowing carmakers to continue using the current emissions methodology. ²

Outside Europe, the findings raise questions about how other jurisdictions count PHEV emissions. The Energy Mix notes the EU studies do not evaluate PHEV driving behaviour in Canada, where automakers have relied on PHEVs toward zero-emissions vehicle targets under a federal EV mandate delayed one year by the government of Prime Minister Mark Carney. Adam Thorn, director of the Pembina Institute's transportation program, told CBC News the findings represent an 'educational opportunity', saying buyers need to recognise 'they're really not going to get the full fuel savings if they don't' charge overnight, while still calling PHEVs 'a key policy to drive down emissions'. ¹

Australian regulators and local real-world fuel use are not assessed in either report, so no conclusions can be drawn here about how Australian PHEV buyers' charging behaviour compares with the European data. What the reporting does establish is that the official lab methodology itself is under active revision in Europe, and that the campaign group's findings and the regulator's own on-board data both point in the same direction: real-world plug-in hybrid emissions are materially higher than current official test claims assume. ¹²