A Bristol brewery is refusing to change the artwork on the can of one of its bestselling beers, despite a ruling by the UK drinks industry’s regulatory body that the cartoon-style animals have “particular appeal” to children.

The design of Lost & Grounded’s Running with Sceptres India pale lager was deemed by the Portman Group to be in breach of its code, which specifies that “a drink’s name, packaging and any promotional material or activity should not have a particular appeal to under-18s”.

The group – funded by the alcohol industry – upheld a single complaint by a member of the public about the prominent use of a line of “cartoony” animals walking in procession up a hill, in the style of illustrations from the Where The Wild Things Are children’s book. A second complaint against another Lost & Grounded beer, Keller Pils – featuring a “cutesy” animal rowing a boat – was not upheld.

Annie Clements, the co-founder of Lost & Grounded, said: “Running with Sceptres is our second-highest selling product and it has taken many years of hard work to gain its current popularity.

“The branding is no different to the multitude of other brands on the market that utilise an artistic style. We operate as a responsible business and would never market products to appeal to under-18s.”

The company said it had never received a complaint, despite both products appearing on national TV and it having thousands of Instagram, Twitter and Facebook followers.

James Calder, the chief executive of the Society of Independent Brewers (SIBA), commented: “Self-regulation of the industry is important and we as producers have responsibilities. But the Portman Group code and (its) independent panel need to understand the need for proportionate regulation based on the likelihood of a product doing actual harm.”

He urged the group to move to “a system where, like other regulators, numerous complaints are needed to trigger an investigation. This ruling will cause significant damage to a brewery with good ethics and business at its core.”

Jenny Watson, the chair of the Portman Group’s independent complaints panel, said: “Lost & Grounded created an engaging can, but unfortunately the panel felt that the prominence of the cartoon animals made it particularly appealing to children. We understand that producers want to use creative illustrators and we would encourage all producers to make full use of our free advisory service before launching a product.”

In what is known as a “retailer alert bulletin”, the Portman Group is now ordering stockists – including Waitrose – to stop selling the beer. It said this situation was unusual, as in the last five years it had handled 80 complaints but issued only seven such alerts.

In a high-profile case, Marks & Spencer last year agreed to change the name of its Porn Star Martini drink because it breached an industry code linking alcohol to sexual activity.