The family of a woman who had a fatal allergic reaction to food bought from Pret a Manger have called for answers over her death.

Celia Marsh, 42, died on 27 December after eating a super-veg rainbow flatbread containing a yoghurt that was supposed to be dairy-free but was found to be contaminated with dairy.

In a statement released on Monday, her family, from Melksham in Wiltshire, said: “We have kept a dignified silence since the death of Celia in December last year as the family has come to terms with her sudden and unexpected death. We are also awaiting the outcome of the investigations into how she died.

“She was a much-loved mother, daughter, sister and wife. We miss her greatly and we just want the answers to why she died after eating lunch with her family.”

Michelle Victor, of the law firm Leigh Day, which is working with the family, said: “We await the full inquest into Celia’s death and will be working with the family for the answers they so dearly need.”

Marsh, a dental nurse who had five daughters, died at the Royal United hospital in Bath after buying the sandwich in a Pret shop in Stall Street in the city.

Her funeral took place in January but a full inquest has yet to be held. A spokesman for the Avon coroner said the results of pathology tests were still pending.

Pret agreed last week to the full labelling of ingredients on all its freshly made products after the case of 15-year-old Natasha Ednan-Laperouse, who was allergic to sesame and died on a flight after eating one of its baguettes bought at Heathrow airport.

Speaking about Marsh’s death, Natasha’s parents, Nadim and Tanya Ednan-Laperouse, said: “We were incredibly saddened to learn of someone else losing their life from allergens in their food. Our hearts go out to the bereaved family.”

After news of Marsh’s death emerged at the weekend, the sandwich chain found itself in a row with its former supplier CoYo, which it blamed for supplying the contaminated yoghurt that was one of the ingredients of the flatbread. Pret said it had been mis-sold the yoghurt, which it said was guaranteed dairy-free but was found to contain dairy protein.

But CoYo, a coconut milk brand that has been endorsed by the TV cook Nigella Lawson, said Pret’s claims that it was to blame were unfounded. It accused the sandwich chain of hampering its own investigation into the death by failing to provide vital information.

“Pret’s inability to provide us with a batch-code, despite several requests, has severely limited our ability to investigate this further,” it said.

CoYo recalled its yoghurts in February 2018 after dairy traces were found. The Food Standards Agency investigated together with Bexley council in London, where CoYo is based, before it issued an allergy alert. CoYo denied that the product recall was related to the death. “The dairy-free product we provided to Pret in December 2017, at the time of this tragedy, is not linked to the product we recalled in February 2018,” a spokeswoman said.

The company would continue to help to find the true cause of the death, she said. “We urge all parties to work together, and not to speculate on the cause of this tragic death, which is unknown as far as we are aware and is still being investigated by the coroner’s court.”

Bath council told Pret about the incident and the chain said it withdrew all affected products. The firm said it had ended its contract with CoYo and was taking legal action.

In a statement, Pret said: “Subsequent testing by Pret and two independent authorities found that the CoYo dairy-free yoghurt contained traces of dairy protein. This is believed to have resulted in the tragic death of a customer from an allergic reaction in December 2017.

“Our deepest sympathies are with the family and friends of our customer in this terrible case and we will seek to assist them in any way we can.”