TL;DR: Plug-in hybrids (PHEVs) promised cheap motoring – but drivers are burning 300% more petrol than claimed, costing £985 yearly instead of £530. ECIU calls it a “dieselgate-style scandal” as sales boom 35% to 225k units last year. Why the massive gap? Most owners skip charging, guzzling pricey petrol.
The long-standing joke about the gap between a car’s advertised fuel economy and its on-the-road reality has taken a serious turn. Recently published data shows that plug-in hybrid real-world fuel consumption isn’t just slightly off—it’s approximately three times higher than what manufacturers are claiming.
While glossy brochures might promise an incredibly frugal 1 to 2 litres per 100 kilometres (equivalent to 141-282 MPG), the reality of daily driving in the UK is closer to 6 litres/100km (around 47 MPG). This staggering 300% difference between PHEV fuel efficiency vs manufacturer claims is now attracting serious attention from the EU Commission.
What’s behind this huge discrepancy?
The answer lies in how often the petrol engine actually fires up. The latest Fraunhofer Institute PHEV study reveals that the combustion engine is doing far more work than official lab tests suggest, a key factor in the growing plug-in hybrid emissions gap UK drivers are experiencing.
We’ve been told these cars are the perfect ‘green’ bridge to full electric vehicles. But in the real world, simple actions like turning on the heater on a cold morning or needing a quick burst of acceleration to merge onto a motorway can trigger the engine.
Data collected from 2021 to 2023 shows a wild variation in performance across different car brands. Interestingly, the analysis found that high-end luxury brands were often the thirstiest. The Porsche hybrid fuel economy performance, for example, showed their models averaged around 7 litres/100km, which is only about 40 MPG.
But wait, it’s not all bad news. More affordable models from manufacturers like Kia, Toyota, Ford, and Renault performed significantly better. In some cases, these cars used up to 85% less fuel than their premium-badged counterparts. It certainly makes you question whether you’re paying a premium for brand performance or genuine efficiency.
The high PHEV combustion engine trigger frequency is at the heart of the real-world vs official EU fuel consumption debate. When researchers confronted Porsche about these figures, the company cited its adherence to ‘legally prescribed measurement procedures’. In plain English, they’re playing by the lab-test rules, even if those rules don’t reflect a rainy Tuesday commute in Birmingham.
Because of this glaring gap, experts are now pushing for changes to EU CO2 emission limit regulations. The proposal is for CO2 penalties to be calculated using wireless data from real cars on the road, not from artificial lab conditions. If EU regulators adopt this approach, some of the biggest names in the car industry could face massive fines for the discrepancy. For now, if you’re considering a plug-in hybrid, remember its real-world fuel consumption depends entirely on your right foot and, it seems, which badge is on the bonnet.
By Mathilda Bartholomew | February 19, 2026
