The warning comes from Fuel Card Services following a recent Which? report that indicated only 13 of 200 tested vehicles living up to manufacturers’ official mpg figures. The report revealed that manufacturers’ official consumption figures were optimistic, on average, by 13%.

The figures appeared during the same month as a report from RAC Business which found that of 1,000 business decision-makers surveyed, 44% cited fuel economy as their top priority when acquiring new vehicles.

Steve Clarke, group marketing manager for Fuel Card Services, said: “The only sensible option is for fleet managers to rely on their own fuel consumption evidence, while ensuring that they continue to refuel vehicles as cost-effectively as possible.”

Clarke also welcomed the eventual implementation of a more reliable testing protocol for fuel consumption, the Worldwide Harmonized Light Vehicles Test Procedure, which may be implemented across the EU during the coming two years.

“While fleet managers wait for consumption figures that can be trusted, they should re-evaluate their fuel procurement. Many will have been using the same fuel cards for years, not realising how that market has changed significantly. They need to reassess, comparing everything available. It makes no sense to look for fuel-efficient vehicles but not to refuel them cost-effectively.”