A teenager had a fatal reaction after unwittingly eating buttermilk at burger chain Byron, an inquest has heard.
Owen Carey, who had a dairy allergy, was celebrating his 18th birthday when he collapsed on 22 April 2017.
Earlier, he had ordered skinny grilled chicken at the O2 Arena branch, but the menu contained "no mention" of a marinade, the inquest heard.
Technical manager Aimee Leitner-Hopps said a notice on the menu asked customers to advise staff of allergies.
She also told Southwark Coroner's Court all waiting staff underwent allergy training.
The inquest heard Mr Carey started to experience symptoms after leaving the restaurant, before he collapsed outside the London Eye.
He died later at St Thomas's Hospital in central London.
Clodagh Bradley QC, representing the Carey family, of Crowborough, Sussex, said regulations required allergy information in a restaurant to be clearly visible.
Information on the Byron menu was "at the very bottom, in a really very small font, in black print, on a royal blue background" making it difficult to read, she added.
Ms Leitner-Hopps said: "It's perfectly legible in my opinion."
She also said it complied with legal obligations.
When asked by assistant coroner Briony Ballard why it could not be more prominent, she replied: "The expectation is that a customer with an allergy should inform us."
Ms Leitner-Hopps said there had been numerous local authority visits over the years to the restaurant but they had "never been told" the wording was not clear enough or was too small.
Ms Bradley QC also said: "The menu makes no mention at all of marinade. It would be very easy for a reader of the menu to think this was a plain grilled chicken breast."
Ms Leitner-Hopps said: "If you have an allergy you should be asking for information and the team would have provided it."
Since Mr Carey's death, she said, and subsequent 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.
Dr Robert Boyle, consultant paediatric allergist at St Mary's Hospital, Paddington, told the inquest there had been about 150 deaths like Mr Carey's in the UK in the past 25 years.
He said: "Fatal food anaphylaxis is uncommon and it is very fast. Typically people die 30 to 40 minutes after they have eaten the food."
He said the subject was poorly understood and called for a national register to gather information on it.
The inquest heard Mr Carey was not carrying his Epipen at the time, but Dr Boyle said it was "unlikely" that an Epipen would have made a difference.
Pathologist Andreas Marnerides gave the medical cause of death as asthma exacerbation caused by food-induced allergic reaction, or anaphylaxis.
He said he would "not disagree" to putting food-induced allergic reaction as the primary cause.
The inquest heard Mr Carey ate half of his chicken before he felt his lips tingling and experienced stomach problems.
He collapsed 55 minutes later.
Members of the public, including an RAF doctor, tried to revive him but when paramedics arrived he was "silent, not breathing and pulseless", the hearing was told.
The inquest continues.