The boss of Byron restaurant says he has not been able to contact two waiters who were on shift when teenager Owen Carey died from an allergic reaction.
Speaking to ITV News Simon Wilkinson said the company had no phone number for the former staff members and they didn't respond to emails.
One of them may have served Owen Carey who died after eating grilled chicken with buttermilk which wasn't listed as an ingredient on the menu.
Byron said it only found out about the case 11 months after Owen visited the restaurant.
That time delay really didn't help either party. CCTV re-records after six months so we had no CCTV evidence of who served Owen and his family. We do know three waiters were working that day - two have returned to Australia. The third waiter we showed pictures of Owen and his family and he didn't recognise them - we serve 120,000 customers a year in that particular branch. A lot of factors meant we just had no evidence. We couldn't bring a waiter into the Coroner's Court and ask what happened?
Mr Wilkinson said he wasn't worried the waiters could still be serving customers in other restaurants.
They [the waiters] could still be serving people. I think that comes back to the training because all our people are trained. Not only do they go through the allergen process and they sign off on that - they shadow someone for a week. I don't have any concern that those people are out in the hospitality industry we just could not contact them.
A coroner ruled Owen Carey was misled into believing there were no allergens in his meal at Byron.
The teenager suffered a fatal reaction after eating grilled chicken coated in buttermilk at the restaurant at the O2 Arena in Greenwich in April 2017 while celebrating his 18th birthday.
The family of Mr Carey have called him their "shining light" and are calling on the Government for 'Owen's Law' to force restaurants to have clear information about allergens on each individual item on the menu.