A teenage girl from Fulham who died after suffering a severe allergic reaction to a Pret a Manger baguette said "Daddy, help me" as she struggled for breath, an inquest has heard.

Natasha Ednan-Laperouse, a 15-year-old with numerous allergies, collapsed on a British Airways flight from London to Nice on July 17, 2016.

She had been travelling with her father and best friend when she stopped to get an artichoke, olive and tapenade baguette as they passed through Heathrow Airport's Terminal 5.

Unknown to the group, the sandwich dough contained sesame seed, a detail not mentioned on its packaging, according to a statement from her father, Nadim Ednan-Laperouse, read on the first day of her inquest at West London Coroner's Court.

Natasha Ednan-Laperouse was on a flight to France when she became ill (Photo - Family Handout/PA Wire)

Natasha was allergic to the ingredient and suffered a cardiac arrest despite two epipens being applied to her legs. She was declared dead the same day at a Nice hospital.

The family's lawyer, Jeremy Hyam QC, became emotional as he read Mr Ednan-Laperouse's statement to the inquest on Monday, at one stage pausing to regain composure.

It said: "How could it be that such a terrible thing could have happened when we were so careful with food?"

Natasha suffered from food allergies her entire life, but had learnt to diligently scrutinise food labels and was alert to the dangers of cross-contamination.

"Before the holiday to Nice, there has never been an occasion when Natasha had failed to respond to the epipen injections and I don't recall being given any advice about what to do when epipen didn't work," her father's statement said.

The group had gone to the Pret branch at 7am, around one hour before they were due to fly.

"Natasha told me she had found a baguette that contained all the ingredients she loved and could eat," her father's statement said.

The label gave "no indication or mention that sesame seeds were present", he said, adding: "Natasha and I relied on food information and saw no need to ask Pret counter staff if any other information was needed."

Oliver Campbell QC, representing the chain, said at the hearing that a label on the sandwich would have said "freshly prepared with good natural ingredients".

Natasha at first felt her throat growing itchy and took some piriton.

Around 20 minutes into the flight, she complained it was getting worse and her father noticed her neck looked red, as if she had been rubbing it.

Shortly afterwards she returned from the toilet with vicious red hives on her midriff "like a jellyfish sting", the inquest heard.

Giving evidence on Monday, her father said: "[She told me] 'Daddy, I'm not feeling well' and she lifted up her top and she displayed these red welts like lacerations which I had not seen before, but I understood something unbelievable was going on."

She was rushed to the cabin's toilets, where her father applied an epipen.

The statement said: "We waited a couple of minutes to see how she reacted.

An inquest into Natasha Ednan-Laperouse's death started today (Photo - Family Handout/PA Wire)

"She said she couldn't breathe properly and it was getting worse and urged me to get the second epipen right away."

He quickly jabbed the second epipen into her upper thigh, but it failed to relieve the symptoms.

The statement added: "Natasha said that she still couldn't breathe and desperately looked at me, she said 'Daddy, help me, I can't breathe'."

She soon lost consciousness and cabin staff were aided by a junior doctor in applying CPR for the remainder of the journey.

Her father was at her side throughout, while her friend Bethany held her hand.

He recalled being "totally focused on saving her life" and "begging her to fight and live".

As hope began to fade that Natasha would survive in hospital, her father put a phone to her ear so her mother and brother could say goodbye.

Her mother Tanya could be seen wiping her eyes as she listened to the statement.

"The pain and agony of the call was beyond anything I have known," the statement said of the moment Mr Ednan-Laperouse broke the news to Natasha's mother.

He continued: "These calls I had to make were the worst of my life. Each of them was completely overwhelmed, distressed and shocked."

Mr Ednan-Laperouse then called his own mother and asked her to visit a branch of Pret a Manger in west London to examine the sandwich.

Finding nothing on the label or on the shelf, his mother made inquiries at the counter and was handed a folder of information.

"My mother looked down the list and found that the baguette dough had sesame seed inside it," the statement said.

"I was stunned that a big food company like Pret could mislabel a sandwich and this could cause my daughter to die."

Mr Campbell suggested on Monday that Natasha's father "must unfortunately be mistaken" about his recollections of the food's packaging, saying they do not typically display ingredients.

Natasha Ednan-Laperouse was just 15 when she died (Photo - Family Handout/PA Wire)

However, Mr Ednan-Laperouse responded that, while he never bought food from Pret, he would regularly go inside branches to inspect the food and found some did have such labels, while others did not.

He added: "There was no label on the fridge, I have got an eagle eye for such things.

"The vigilance levels that me and my wife have are like that of a hawk - if there is some there to be seen, we are going to be seeing it."

Natasha had been travelling to Nice for a four-day break with her best friend at the start of what should have been "the best summer ever", her parents said in an earlier statement.

The inquest is due to last until Friday.