The family of a teenager who died of an allergic reaction to an unlisted ingredient in a burger have called for a new law on allergen labelling in restaurants.

Owen Carey suffered anaphylactic shock after eating grilled chicken marinaded in buttermilk at the Byron restaurant at the O2 Arena in Greenwich, despite telling staff that he was allergic to dairy products.

A coroner ruled on Friday that the restaurant’s menu misled Carey into thinking the burger was safe for him to eat by failing to highlight that the dish contained buttermilk.

Assistant coroner Briony Ballard, sitting at Southwark coroners court, called Carey’s death a tragedy.

“The deceased made serving staff aware of his allergies. The menu was reassuring in that it made no reference to any marinade or potential allergenic ingredient in the food selected,” she said.

“The deceased was not informed that there were allergens in the order. The food served to and consumed by the deceased contained dairy which caused the deceased to suffer a severe anaphylactic reaction from which he died.”

In a statement outside the court, Carey’s family called for new rules on allergen labelling. “We want restaurants to have to display clear allergen information on each individual dish on their menus,” they said. “The food industry should put the safety of their customers first.

“It is simply not good enough to have a policy which relies on verbal communication between the customer and their server, which often takes places in a busy, noisy restaurant where the turnover of staff is high and many of their customers are very young.

“This leaves far too much room for error on an issue we know all too well costs lives. We hope that we can bring about change with ‘Owen’s law’ for better allergen labelling in restaurants.”

Carey, from Crowborough, East Sussex, who was studying for his A-levels, had been on a day out with his girlfriend in London to celebrate his 18th birthday on 22 April 2017. They had visited the Stars Wars exhibition at the O2 before stopping to eat at Byron.

He ate half of his skinny grilled chicken burger with no sauce before beginning to feel symptoms of an allergic reaction. The couple had planned to go on to visit the London Aquarium in Waterloo, but Carey collapsed in his girlfriend’s arms yards from the attraction. Paramedics gave first aid but he died at nearby St Thomas’s hospital 45 minutes later.

The inquest hear that Carey usually carried an EpiPen, but that on that day he had forgotten it.

The court heard on Thursday that, at the time of Carey’s death, Byron’s menu did not mention that the chicken in the burger he had ordered was marinaded in buttermilk.

Clodagh Bradley QC, representing Carey’s family, argued the omission could make a customer believe it was a plain chicken breast. She also suggested that allergy information, which at the time was positioned on the back of the menu, was difficult to read, pointing out that it was in black print against a blue background.

Byron’s technical manager, Aimee Leitner-Hopps, who is responsible for ensuring teams are fully trained in food safety, said that allergy information on the menu met industry standards at the time.

“If you have an allergy you should be asking for information and the team would be able to provide that information in the allergy guide,” she said.

“I think most businesses were taking the same approach that the customer would inform the restaurant about allergies,” she said, adding the restaurant had been visited by local authority officials many times over the years and had never been told the wording was not clear enough or too small.

Leitner-Hopps said all staff at the time received online allergen training, which required them to tick different sections, and on-site training. “It was apparent to me training available to the teams was sufficient,” she said.

Byron’s chief executive, Simon Wilkinson, offered both the company’s and his own deepest condolences to Carey’s family. “We take allergies extremely seriously and have robust procedures in place,” he said.

“Although those procedures were in line with all the rules and guidelines, and we train our staff to respond in the right way, it is a matter of great regret and sadness that our high standards of communicating with our customers were not met during Owen’s visit.

“We believe that Byron always did its best to meet our responsibilities, but we know that this will be of no comfort to Owen’s family.”

Carey’s case echoed that of Natasha Ednan-Laperouse, 15, who collapsed on a flight to France in 2016 after eating an unlabelled Pret A Manger sesame seed baguette at Heathrow airport and later died in hospital.

Her parents called Carey’s inquest a “landmark judgment for millions of allergy sufferers in this country” and said they saw remarkable parallels between Carey’s death and that of their own daughter.

“With around 8% of children in this country now having allergies, we are facing an epidemic,” Nadim and Tanya Ednan-Laperouse said in a statement.

“The food industry should be leading the charge for better information for its millions of customers with allergies, not hiding – as has Byron Burgers – behind corporate legal-speak of being ‘industry standard’ or ‘meeting our legal obligation’.”

After the inquest, Carey’s mother, Moira, paid tribute to her son. “Owen had a load of energy and was always smiling, and wanted to get to the most out of life,” she said.

His father, Paul, said he would always think of the times he had together with his son. “He was an excellent chap, a beautiful boy and a great mate,” he said.