The ad featured Gary Rhodes, as he conducted an informal survey to discover how many people preferred the taste of Flora Buttery to the leading spreadable from a butter brand.
Text shown on-screen stated: Out of 200 people tested 48% preferred Flora Buttery Taste, 45% Lurpak Lighter spreadable, 7% had no preference.
Arla Foods and 29 viewers challenged whether the ad was misleading as the results it presented were marginal and thus too small on which to base the preference claim.
The ASA concluded that the evidence provided was not substantial enough to support the claim that more people prefer the taste of Flora Buttery.
The ad must not be broadcast again in its current form.
Tha ASA also ruled against a radio ad for Weight Watchers, after one listener, a GP, complained that it was misleading.
The ad stated: "Stop Diets, Start Weight Watchers". The complainant said that Weight Watchers involves eating plans which control and restrict food intake and is therefore a type of diet.
The ASA concluded that the ad was misleading and must not be broadcast again in its current form.