New research suggests that drivers who spend a lot of time on motorways may be better off buying a diesel car than a hybrid model.
Experts at Emission Analytics found that hybrid cars are far less fuel-efficient than diesel vehicles when cruising or accelerating at higher speeds.
They said this is because developers of hybrid vehicles usually focus on the battery rather than the engine, which typically uses petrol rather than diesel.
However, the researchers confirmed that hybrid cars are far more suitable for urban driving at low speed than petrol or diesel options, as they allow drivers to accelerate gently and can recapture some of the energy that is generated when the driver brakes.
They warned that because most cars are tested at these low speeds, many motorists may end up buying a hybrid wrongly believing it will give them more miles per gallon no matter at what speed they drive.
Study leader Nick Molden, from Emissions Analytics, said drivers should be aware that hybrids "have a particular role to play", especially for urban driving, but that a diesel car could be a better option for some motorists.
He added that hybrids are often presented as being "unquestionably a good thing" but that is not necessarily the case.
Copyright Press Association 2014