Campaigners have branded the decision of some food manufacturers not to use a colour-coded labelling system on cereals as "scandalous".
Action on Sugar, based at Queen Mary University of London, is calling for "traffic light" front of pack (FOP) nutrition information to be introduced across all food and drink products.
But it says that many manufacturers are not using the Department of Health-endorsed system, despite their products containing high levels of sugar which would attract a red label.
The group surveyed 25 cereal manufacturers and found that while Bear, Jordans, Kellogg's and Nestle do use FOP labels, they are not colour-coded.
Kellogg's Crunchy Nut Honey and Nut Clusters, Eat Natural Toasted Muesli Vine Fruit and Jordans Country Crisp with Crunchy Chunky Nuts were highlighted as some of the cereals that would have a red label for sugar content.
Action on Sugar said this makes it very difficult for consumers to interpret the information and make informed decisions.
It also found that a further six brands, Eat Natural, Lizi's, Nature's Path, Paleo Foods Co., Rude Health and Dorset Cereals, contain no FOP nutrition labelling and some products contain high levels of sugar.
Katharine Jenner, Action on Sugar and FoodSwitch UK campaign director, said: "Shoppers should be seeing red, and they would be if manufacturers used the correct labels.
"It's scandalous that certain food manufacturers are still refusing to be transparent when it comes to front of pack nutrition labelling.
"If there is no front of pack label with one brand, shoppers should assume they are hiding something - so buy another brand instead."
The sugar and health expert group says that cereal shoppers could save themselves around 45 teaspoons of sugar per month (182g) if they had access to consistent FOP labelling.
Registered nutritionist Kawther Hashem, researcher at Action on Sugar said: "Consistent labels allow shoppers, at a glance, to see the huge variation in salt and sugar levels in breakfast cereals.
"Many of these cereals, often aimed at children, would receive a red traffic light label for being high in sugars.
"Companies need to reduce the sugar and salt levels now by working towards the sugar targets by 2020 and salt targets by the end of 2017 - and proudly display this on their front of pack nutrition labels."
The colour-coding uses red for high, amber for medium and green for low on labels to indicate to consumers what levels of fat, saturated fat, sugars and salt are in the product.
A spokesman for Kellogg's said: "Kellogg's complies with all EU and local labelling requirements, which set out specific rules regarding what information should be included on food labels.
"We strive to present this information in a way that is both legally compliant and clear and meaningful for consumers. Kellogg was one of the first companies to voluntarily adopt front of pack GDA labelling back in 2007.
"We use GDA labelling because we believe it gives consumers a better source of information than traffic light labels. Traffic light labelling does not take into account portion size or the role that the food plays in the diet.
"Kellogg's is committed to improving the nation's diet. Our long-term sugar reduction programme has already seen sugar come down in some of our biggest brands while removing 2,000 tonnes of sugar from the nation's diet by the end of 2017."