An executive at a fast food chain where a teenager suffered a fatal reaction to a burger has told the inquest into his death that he should have asked about allergens when he ordered it.

Owen Carey died after eating a chicken burger that contained buttermilk at the Byron restaurant at the O2 Arena in Greenwich, southeast London, where he was celebrating his birthday with his family. He was allergic to dairy.

The 18-year-old began experiencing symptoms after leaving the restaurant on 22 April 2017 but got as far as the London Eye, near Waterloo in central London, before collapsing. He died at nearby St Thomas’s hospital 45 minutes later.

Southwark coroners court heard on Thursday that Carey had ordered a skinny grilled chicken burger with no sauce from the O2 Byron branch. The menu did not mention that the chicken was marinated in buttermilk, the court was told.

A postmortem showed he had suffered an anaphylactic reaction.

Clodagh Bradley QC, representing Carey’s family, from Crowborough, East Sussex, argued the omission could make a customer believe it was a plain chicken breast. Bradley 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.

But Aimee Leitner-Hopps, Byron’s technical manager, 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 (their) 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 was too small.

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

Nevertheless, since the incident, and following research showing one in 10 people aged 16 to 24 hide their allergies, staff now ask customers directly if they have any allergies or dietary requirements, she said.

When customers reveal an allergy, staff press a button that highlights the word “allergen” on the order ticket, along with space for more details, the inquest heard. Staff are then expected speak directly with the kitchen team to ensure the allergy information has been received.

Coroner Briony Ballard said she would not read out the report of the restaurant’s head chef as the “error” appeared to lie at the “point of ordering and not at the back of the house”.

Carey had been due to visit the Sea Life Aquarium after visiting the Star Wars exhibition at the 02 Arena earlier in the day. He usually carried an EpiPen but had forgotten it.

The inquest continues.