Celia Marsh died almost five years ago after eating a Pret a Manger sandwich at a branch in Bath. Today, the inquest into how it happened began.

Marsh, a dental nurse and mother of five, suffered an anaphylactic reaction after eating a £3.75 “super-veg rainbow flatbread” with her family in December 2017. It was supposed to be dairy-free.

The inquest is not a criminal trial. As Maria Voisin, the coroner in charge of the case, said last month, inquests are about “fact-finding, not fault-finding”. While Pret was initially charged by Bath & North East Somerset Council with food safety failures, this was dropped due to a lack of evidence.

The inquiry over the next three weeks will focus on the circumstances around Marsh’s death. Namely, how did a supposedly vegan yoghurt end up containing deadly traces of dairy?

The answer to that question could have wider implications for the rest of the food sector, if the inquest suggests further measures are needed to prevent such allergen-related deaths in the future.

Major improvements have already been made in this area since the cases of Celia and fellow allergy sufferer Natasha Ednan-Laperouse, who died after eating a Pret baguette containing sesame in 2016.

Following tireless campaigning from the latter’s parents, the UK government enacted Natasha’s Law last year to make businesses legally obliged to label all pre-packed food with a full list of ingredients and potential allergens. Before this law, there was always an exemption for sandwiches and foods prepared on site.

Celia Marsh’s inquest may well inspire further action, particularly when it comes to preventing errors in earlier stages of the supply chain. It is believed the issues with Marsh’s flatbread stemmed from a mismatch in the information passed from CoYo, the Australian coconut-based yoghurt manufacturer, to Planet Coconut, the UK distributor that supplied Pret. (However, CoYo has questioned Pret’s claim that its yoghurt was the cause of the allergic reaction.) Further information on this chain of events should emerge next week, when the inquest will hear a statement from CoYo founder Henry Gosling, alongside testimony from other suppliers.

It seems clear that unless comprehensive allergen information is held and communicated between parties, the ability of retailers such as Pret to ensure full and correct labelling is severely compromised.

As Jamie Cartwright, a partner at Charles Russell Speechlys, points out, there are currently no legal protections in place to ensure this happens. “Natasha’s Law responded to a perceived lack of accessible information on ingredients for consumers on the product itself. It does not deal (nor was it intended to deal) with the broader risks from manufacturing through to fork or counter.”

The inquiry is likely to examine these risks, alongside other questions. There is talk of it examining ‘may contain’ allergen labels, as Marsh’s family is understood to be frustrated by their prevalence and ambiguity.

Earlier today, Tanya Ednan-Laperouse, Natasha’s mother and founder of the Natasha Allergy Research Foundation, said it was vital to get full disclosure from all the companies involved to ensure a thorough understanding of what happened in the supply chain and how that led to Marsh’s death. “Only that way can the lessons be learned to help halt the tide of food allergy deaths in this country.”