M&S brought the complaint over the two ads, which carried the claim: "Iceland Luxury Sourdough Crumpets are better than M&S Ultimate Five Grain Crumpets for overall quality."
M&S questioned whether the claim was verifiable, and whether it was misleading and could be substantiated.
Both ads featured an explanation of the basis of the claim: a blind taste test of 58 people, in which 79% had rated Iceland’s crumpets as good or excellent, while only 62% had done so for M&S.
The ASA said that the sample size was not large enough to have confidence in the results. It also said that because the test participants were not asked to directly compare the two products, the results did not reflect a preference for Iceland’s crumpet.
The watchdog said that while the claim could be verified, it had not been properly substantiated.
Iceland was found to have breached the CAP Code rules on misleading advertising, qualification, exaggeration and comparisons with identifiable competitors, and the ASA ordered the ads not be used again in the form complained about.
Both crumpets sell at £1.00 for a pack of six.