New data has revealed that tens of thousands of hybrid cars bought with government grants over the past seven years may have burned as much fuel as regular petrol engines.
The plug-in hybrids (PHEVs) were available to be bought at a discounted rate due to a government incentive introduced in 2011, which gave buyers up to £4,500 off new cars.
It led to the UK becoming the biggest market in Europe for PHEVs, although the majority of eligible vehicles were bought by company fleets.
Now, data from The Miles Consultancy, has revealed that vehicles they tested had averaged around 40 miles per gallon (mpg), some way off the advertised 130mpg.
The Miles Consultancy, who advise 300 blue-chip companies on fuel management, have found that mileage records for 1500 models showed an mpg of just 39.27, while the manufacturers had said they could reach 129.68 on average.
Data for mpg of 2432 hybrids vehicles was also collated and showed an average of 49.06mpg, still considerably lower.
The firm believes that many companies used the government grant to save on buying regular cars for their fleets and claim that many owners probably never even unwrapped their charging cables.
Around 70 per cent of this year's 37,000 hybrids sold were bought by businesses, but the scheme has been recently scrapped.