The poster, captioned "Vote New Cadbury's Caramel McFlurry", shows a shot of the dessert alongside the Cadbury's Caramel and McDonald's logos.
However, the dessert contains McDonald's own caramel sauce.
McDonald's explained that the caramel sauce used in the McFlurry was made to a recipe that had been approved by Cadbury's.
The confectionery giant claimed that it "sets out criteria for each of its licensed products, so that they attain the same product attributes as the equivalent Cadbury's product".
The ASA, however, rejected the explanation and found McDonald's guilty of misleading advertising. Because there was a picture of a Cadbury's Caramel on the poster, the ASA said consumers would expect the McFlurry to contain
the same caramel sauce as the chocolate bar.