“Tashi, I love you so much, darling. I’ll be with you soon. I’ll be with you.”

These were the last words that Tanya Ednan-Laperouse spoke to her daughter, Natasha, who lay dying 800 miles away in a hospital in France.

Tanya’s husband, Nadim, had placed his mobile phone on the pillow by their daughter’s ear when it became apparent that the 15-year-old, who had suffered a catastrophic allergic reaction after eating a Pret a Manger baguette, was not going to live. “You’ve got to say goodbye to her now,” Nadim urged his wife, who was waiting at Stansted airport for a flight out to be at their daughter’s side. “Don’t lose time. She’s going to die any minute. Say something. Do it right now. She might hear it.”

Natasha’s parents broke their silence on Saturday to reveal their final minutes with their daughter after a five-day inquest that is expected to trigger a major shake-up in food safety regulations and the emergency treatment of people suffering severe allergic reactions.

Coroner Dr Séan Cummings criticised the sandwich chain for failing to properly alert customers to potentially fatal allergens, warning that its signs were “inadequate”.

In July 2016, Natasha, who was extremely allergic to sesame, bought an artichoke, olive and tapenade baguette from a Pret store at Heathrow airport. It did not have any allergen advice on its wrapper because, as it was made on the premises, it was not required by law.

Cummings said he would be writing to the company and to Michael Gove, the secretary of state for environment, food and rural affairs, calling for an overhaul of the current labelling system. Natasha’s family are now considering launching a civil claim against Pret.

Facebook Twitter Pinterest Natasha’s parents, Tanya and Nadim Ednan-Laperouse. Photograph: Ian McIlgorm

“We now know she didn’t die on our watch,” her mother said. “She died on Pret’s watch, and all thanks to the absence of two little words on the packaging of her sandwich. If the label had listed sesame seeds Natasha wouldn’t have touched it and she’d still be alive.”

Natasha’s father, who injected his daughter with adrenaline from two EpiPens as she became unwell having boarded a British Airways flight to Nice for a holiday, said he blames himself for her death “because I love my daughter – I really love my daughter, in a way that’s like one flesh. As a parent I would die a thousand times, crucified, for her to live. I spent 15 years nurturing the most precious thing in my entire life. As a human being, there’s nothing more important than that. In that moment, how could it be that I failed her? I will live with that until I die.”

He described seeing his daughter in the mortuary. “You go into a cubicle and she was lying there, stone cold. She’d been in a fridge. It didn’t look like her. It wasn’t her. Where was she? I hugged and kissed her. The shape’s the same but the colour’s wrong. She was gone. You really believe in a soul when you see that. But her body was all I had left.”

Tanya said they had not been able to touch Natasha’s room. “Her clothes are still on the floor. Her homework’s on the table. We haven’t unpacked her school bag or the bag she took that day.”

Her clothes are still on the floor. Her homework's on the table. We haven't unpacked her school bag or the bag she took that day Tanya, Natasha's mother

The couple’s decision to speak out came as it emerged that the coroner would be writing to the Medicines and Healthcare Products Regulatory Agency and the manufacturer of EpiPens to highlight issues relating to their dosage and needle length. At the inquest, an expert witness explained that the technology was “developed for the first Gulf war to give antidotes to chemical warfare” and was initially meant to be used on “lean male army recruits”.

The inquest heard how both the EpiPens used on Natasha had 16mm needles and contained 300 micrograms of adrenaline. Even some individuals of normal weight and BMI (body mass index) might find a 16mm needle insufficient for the adrenaline to reach their muscle, the inquest heard. According to Resuscitation Council guidance “a 25mm needle is best and suitable for all ages”.

The expert explained that it was unclear how much adrenaline had entered Natasha’s system but noted that people suffering anaphylaxis in hospital were given 500 micrograms in a single dose in severe cases.

In the year before Natasha’s death, the inquest heard that Pret had been contacted by other customers who had suffered severe allergic reactions.

“The coroner found that Pret’s procedures for recording and monitoring reports of problems with foods or items purchased at Pret were inadequate and incoherent,” said Jill Paterson, of law firm Leigh Day, which represented Natasha’s family.

“They screwed up, yes,” Tanya said of Pret. “But they could lobby for change to our labelling laws. They could help this happen. Now they know it can’t continue. If they try to they’ll have a big fight on their hands, certainly from us.”