Allergy sufferers are at risk after potentially fatal ingredients were discovered in samples from takeaways, restaurants and food manufacturers across Suffolk.
New research shows that more than 25% of food samples tested by Suffolk Trading Standards were found to have hidden allergies from 2016 to 2019, with no indication that an allergen was present.
Out of 187 food samples taken, 47 contained traces of allergenic substances that could prove harmful or even fatal to food allergy sufferers - such as coeliacs, people with nut allergies and those with a dairy intolerance.
Of the undeclared allergens found, traces of peanuts, gluten, milk, mustard, eggs and sulphites were all discovered in Suffolk eateries.
The research, carried out by Unchecked.uk and the Times, found that more than 20% of samples contained traces across England.
Food Standards Agency figures also show that around 10 people die in the UK each year as a result of undeclared allergenic ingredients.
Suffolk County Council are reassuring customers that they take food allergens "very seriously" and have continued to keep their tests consistent over the last few years.
A spokesman for Suffolk Trading Standards, said: "Our Trading Standards officers regularly work with local businesses in Suffolk to help them be compliant when it comes to food allergens.
"Every year we take around 200 food samples, primarily from takeaways, restaurants and food manufacturers, to see how they're doing."
Sometimes the council's visits will be routine spot-checks, but other times they "respond to concerns" they receive from customers.
The spokesman continued: "If we do find a sample which contains an allergen when it shouldn't, we'll work with the business to help them put things right and we will revisit them until we're satisfied they have resolved the issues.
"We take food allergens very seriously and encourage any customers who think they may have purchased food containing unexpected allergens, to let us know by contacting the national Citizens Advice service on 03454 040506, or through our social media accounts."
The proportion of failed results will be higher than if it were random testing, as Suffolk County Council targets poorly performing food businesses, or takes samples following tip-offs from the public where someone may have suffered a reaction.
Doctor Hazel Gowland, leading expert in food allergy risks, says sample testing is "critically important".
"The presence of unlabelled allergens in a range of foods is potentially life-threatening for increasing numbers of consumers with allergies, intolerances and coeliac disease," she said.
"Sampling by local authority food officers and testing by public analysts are essential to ensure food is safe and labelling is correct.
"These results are a major concern, indicating the urgent need for additional local authority resources to protect consumers."
Researchers say the problem is likely to go even further than the figures indicate, as despite a number of high-profile food allergy deaths in recent years, the number of food samples tested for allergens fell by over a quarter during the period of 2016 to 2018, with 20 UK Local Authorities taking no allergen samples at all.
However, Suffolk County Council continues to test around 200 samples every year and is committed to ensuring local businesses are compliant when it comes to food allergens.
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