The peanut has become a problem.

Mars Wrigley, the confectionery giant, has learned that one of its most familiar advertising assets — the yellow M&M character, who has been selling candy since the Eisenhower administration — may no longer appear in certain British advertisements because regulators have determined that he looks too much like the product he represents.

In a ruling issued Tuesday by the Advertising Standards Authority, the British advertising watchdog found that the yellow M&M character, with his distinctive oval shape, constitutes an "identifiable" depiction of Peanut M&M's, and therefore violates restrictions on advertising less healthy foods that took effect in January. The complaint was brought by Bite Back, a food campaign group.

The determination is notable for what it does not cover. The green M&M character, who appeared in the same Instagram advertisement, was cleared by the authority because her round shape could represent any number of M&M's variants rather than a specific product. Mars Wrigley had argued that all of its characters — anthropomorphic candies with arms, legs and what the company described as "distinct personalities" — were intended to promote the brand overall rather than any particular item.

The regulator was unmoved. "We considered that, because of their distinct shape, the oval M&M's characters, including the yellow one featured in the ad, depicted Peanut M&M's," the authority wrote.

(One imagines the green M&M, who has weathered previous controversies involving footwear, taking some satisfaction in her continued clearance.)

Three of the brand's seven characters are oval-shaped, meaning they may effectively be barred from British television before 9 p.m. and from paid digital advertising. The characters have appeared in M&M's marketing since 1954 — a run that has now encountered the particular logic of modern food advertising law, in which a cartoon that has promoted candy for seven decades can be deemed too closely associated with candy.

Original story published in Marketing Week: "M&M's brand character gets ad banned under unhealthy food rules"