Citroen based the claim on the results of a refined search of the small family car category for models with automatic gearboxes and diesel engines.

But the ASA considered that viewers would understand the claim referred to a comparison with all cars in the class, in which the Toyota Prius recorded the lowest CO2 emissions of 104 g/km.

The ASA did not believe the on-screen text "Applies to C41.6 HDI EGS" was sufficient to avoid this implication and ruled that the advert should not appear in its current form again.

Another complainant objected to the advertisement on the grounds that it gave the impression that the C4 was more environmentally friendly than it was.

The ASA, however, did not uphold this complaint, concluding that the carmaker was a comparatively low CO2 producer.