Most TV adverts for sweets, crisps and chocolate shown when children are likely to be watching are placed by firms who claim not to promote their products to that age group.

The disclosure, in new research by the University of Liverpool, has prompted claims that food giants such as Mars, Haribo and PepsiCo are in “flagrant” breach of their own codes of behaviour.

The academics found that 80% of all ads for confectionery and snacks shown on UK TV before the 9pm children’s viewing watershed were from those three firms, plus Kellogg’s and Mondelez.

Their analysis of ads shown on 76 channels also revealed that 49% of all such ads are broadcast between 5.30am and 9pm, when viewing by children is at its highest.

“The discrepancy between these company commitments and the large number of their ads aired before the watershed suggests a flagrant disconnect between their marketing policies and what actually happens in practice,” said Rebecca Tobi, the senior business and investor engagement manager at the Food Foundation.

The findings are contained in the thinktank’s annual report, published on Thursday. Its analysis of ads for sweets and snacks shown in July and August 2022 found that 13 different food and drink firms had ads shown during those hours, of which five firms provided 80%.

Haribo accounted for the most – 25% – with ads for products such as Starmix, closely followed by Mars UK (20%) with ads for products such as Galaxy, Snickers, Maltesers and M&Ms. Tobi highlighted that Haribo’s corporate responsibility report says: “Haribo does not advertise in any media primarily directed to children under 16 years.”

Similarly, PepsiCo’s UK-responsible marketing policy states: “We do not promote or market HFSS [high in fat, sugar and salt] products to under-16s across any media.”

The findings illustrate why Labour ministers have decided to ban the advertisement of junk food – anything judged HFSS under its nutrient profile model nutritional assessment rules – on TV before the 9pm watershed, and at any time online, from 1 October 2025.

“This is yet another example of the opaque marketing strategies of some of the biggest players in the food industry and illustrates why the government is right to protect children and young people” said James Toop, the chief executive of Bite Back, the campaigning arm of Jamie Oliver’s organisation.

“These companies have been spending too much money and effort advertising unhealthy products to children.”

Earlier this year, before he became the health secretary, Wes Streeting criticised food firms for using marketing to manipulate people into buying products that contributed to bad diets.

“As citizens we are highly manipulated by the marketing that’s thrown at us. Certainly in terms of children, parents will experience the ordeal of going around the supermarket and being tugged down [by children] to get that KitKat cereal or chocolate bar,” he said in February.

Tobi urged Streeting to force all food firms to disclose what proportion of their sales came from healthy or unhealthy products. While some big firms agree, most are opposed. The last Conservative government considered making such disclosure mandatory, but relented and made it purely voluntary in the face of pushback from the sector.

“Good data drives good decision-making yet ingrained food industry secrecy means, as things currently stand, neither policymakers nor businesses have a clear idea of who is selling what,” Tobi said.

The Food and Drink Federation, which represents major producers, said manufacturers took obesity and poor diet seriously and accepted that they had a role in tackling these issues.

A spokesperson said: “Companies have made significant progress to create healthier options for shoppers, based on government guidelines and the high fat, salt and sugar regulations. Thanks to substantial investment, FDF members’ products now contribute far fewer calories, salt and sugar to the British grocery market than they did in 2015.”

The industry complied with all advertising rules on unhealthy food, they said, adding: “The food and drink industry is open to working with government to consider how we can collectively report on progress in a transparent and consistent way, and we recognise that this is important in gaining a better understanding of the food system.”

The Department of Health and Social Care said: “We are committed to tackling [obesity] head on, shifting our focus from treatment to prevention as part of our 10-year health plan.

“We have already made a strong start by restricting junk food advertising on TV and online, limiting schoolchildren’s access to fast food, and confirming that we will take steps to ensure the soft drinks industry levy (sugar tax) remains effective and fit for purpose.”