A Cornish cider brewer has been told by the Portman Group that its bottle labelling, featuring a grinning, sunglasses-wearing cartoon snake character, breaches its code of conduct and must be changed.

The rattlesnake character, which appears on bottles of Cornish Rattler Cyder, was deemed "irresponsible" by the alcoholic drinks watchdog because it has "particular appeal to under 18s".

The Portman Group's complaints panel upheld a complaint by a member of the public, who described the branding on bottles of Cornish Rattler Cyder as "similar to the cartoon characters Teenage Mutant Ninja Turtles, which are popular among pre-teen children".

The panel upheld the complaint, asserting that the packaging contravened the Portman Group's code, "which sets minimum, mandatory standards for drinks producer marketing".

The ban comes a week after the Portman Group blacklisted BrewDog's Tokyo beer for encouraging excessive drinking.

Healey's Cornish Cyder Farm explained to the panel that rattler is a Cornish variety of cider apple used to brew its Cornish Rattler Cyder. Accordingly, it decided to use a snake image to denote the drink's provenance but wanted to avoid using a realistic image to distance the brand from associations with poison. It therefore opted for a cartoon-style snake – the sunglasses and beach in the background were meant to convey its Cornish heritage.

The company refuted that the snake would have particular appeal to under-18s and stressed the stylistic differences between the character and Teenage Mutant Ninja Turtles.

However, while acknowledging the differences, the panel concluded that the prominence of the snake nevertheless "caused the packaging to have a particular appeal to under-18s", and was in breach of paragraph 3.2(h) of the Portman Group's code.

The West Country cider brewer has since said it will change its marketing to address the panel's concerns, while a Retailer Alert Bulletin has been issued to prevent the sale of the product until its packaging is altered.

David Poley, the group's chief executive, said: "The snake character and the holiday themes were chosen because of the drink's name and Cornish heritage.

"The producer overstepped the mark with its use of cartoon imagery, causing the panel to consider it irresponsible. We're taking action to prevent the sale of the drink in its current packaging."