Saab has become the latest firm to fall foul of the Advertising Standard Authority's crackdown on misleading green ads after the watchdog upheld complaints against an advertisement for its BioPower range of flex-fuel cars.

The national press ad showed two parallel horseshoe prints and tyre marks accompanied by the slogan "More horsepower. And a smaller carbon footprint." The ad went on to claim that Saab's BioPower range used a flex-fuel engine that allows it to run on bioethanol E85, petrol, or a mixture of the two.

It added that bioethanol E85 could reduce CO2 emissions by up to 70 per cent and that "bioethanol consumption does not significantly raise atmospheric levels of CO2 because the CO2 which is released when it is burned is counterbalanced by that which is removed from the atmosphere by photosynthesis when growing crops and trees for ethanol production".

The ad attracted three complaints regarding the claim that bioethanol reduces CO2 emissions by up to 70 per cent and two further complaints against the claim that "bioethanol consumption does not significantly raise atmospheric levels of CO2".

The ASA rejected the first complaint, noting that Saab had substantiated the claim using data from the Energy Savings Trust and a widely accepted methodology for measuring the "wheel-to-well" emissions that found that E85 made from Brazilian sugar cane delivered a CO2 reduction of 74 per cent compared to conventional petrol.

However, it upheld the second complaint, ruling that the ad was "misleading" on the grounds readers were "likely to infer that bioethanol did not add a significant amount of CO2 to the atmosphere", when in fact it still resulted in a 30 per cent net addition to atmospheric CO2.