With its list of soothingly archaic ingredients – burdock, juniper, speedwell – its elegant glass bottles and Victorian labels, the Fentimans range of soft drinks seems to hark back to a more innocent age.

But not everyone finds its wares morally palatable. A transatlantic row has erupted between the Northumberland company and campaigners in the US after a schoolboy in Maine noticed the bottle of Victorian lemonade he was drinking contained 0.5% alcohol and took the offending beverage to the principal's office.

The principal of Houlton High School got in touch with the police and the matter is now in the hands of Maine's liquor licensing officials and the state Attorney General's office.

Two pressure groups – the Aroostook Substance Abuse Prevention Coalition (Asap) and the Maine Alliance to Prevent Substance Abuse (Mapsa) – are now calling for the lemonade to be banned from sale to those under 21 and reclassified as "imitation liquor". According to state law, imitation liquor is any product containing less than 0.5% alcohol by volume which appears to imitate liquor whether by appearance, taste or smell.

Clare Desrosiers, project director for the Asap coalition, said the lemonade contains alcohol and so should not be sold to minors. She added: "To me, it is sold in what looks like a liquor bottle."

The reaction at Fentimans' HQ in Hexham is an odd cocktail of bemusement and gratitude.

"I think it's quite amusing, really," said Eldon Robson, Fentimans' managing director and master brewer.

"Maine is of course where our Puritanical forefathers went because Britain was not strict enough and it has been said that Puritans are people who are always worried that someone, somewhere might be having fun."

The company said it did occasionally receive inquiries about the 0.5% alcohol content of its drinks, which is the result of botanical brewing and a seven-day fermentation process.

It pointed out that its beverages are legally classified as soft drinks, adding that trace alcohol could be found in "bread, mouthwash, orange juice and even chewing gum".

"It's extraordinary that a child taking a bottle of lemonade to the principal should generate this furore," said Tiffany McKirdy, Fentimans' operations manager.

"People online have been highlighting the farcical nature of what's going on - one person said that what alarmed them most was the child who went to the principal. They said he reminded them of the kind of child who tells the teacher that he's forgotten to set the class their homework."

Not that the company is complaining: the row has left its US operation "inundated" with inquires from people in 30 US states and parts of Canada asking where they can buy Fentimans lemonade.

And while McKirdy stressed that underage drinking was a serious issue, she doubted that Fentimans lemonade would become the poison of choice for American teenagers.

"To get the same effect as drinking a pint of 4% beer, you'd have to drink 16 bottles," she said. "You'd be awash or in hospital."