The crunchy, honey-coated cereal, with its garish packaging, will almost certainly appeal to the children but it also seems to be the healthy option. Tesco reassures customers on the labelling that the cereal contains “controlled” levels of both sodium and sugar. A big white tick on the front of the box reinforces the message.

“We’ve kept salt, sugar and additives to an absolute minimum . . . they will not even realise that it’s doing them good,” boasts the packet, which is part of the the Tesco Kids range from Britain’s largest retailer.

Below the blurb is a table of ingredients but, unless she has a calculator, the mother — or shopping father — is unlikely to bother working out that a single bowl of Breakfast Boulders contains the equivalent of 0.5g of salt, a quarter of the recommended daily intake of salt for a three year old.

She may also miss that the cereal consists of 30% sugar. In fact the cereal contains more sugar than 20 other cereals on sale in Tesco that do not claim to have “controlled sugar”.

The misleading Boulders blurb is one of more than 20 incidents of suspected mislabelling that trading standards officers have found in an eight-week period after testing Tesco products. All were recorded in December and January by Hertfordshire trading standards, which collects reports from other trading standards offices around the country. The documents were obtained under the Freedom of Information Act; similar reports for other supermarket chains have yet to be released.

The findings provide only an informal snapshot and Tesco says it continually monitors the quality of the 40,000-odd products it sells to catch anomalies. However, the findings illustrate how labels can be misleading.

According to the documents, Essex county council trading standards officers analysed an own brand Tesco drink — apple and kiwi twist — that claimed to contain “added vitamin C”, which many consumers choose for its perceived health benefits.

The label claimed it contained 4.0mg/100ml of vitamin C. Tests showed it had just 0.2mg/100ml. Essex trading standards department described the result as “uncommon” and said it was investigating with a view to a possible prosecution.

Tesco fresh leaf spinach had almost 4,300mg of nitrate per kilogram, almost double the maximum permitted level of 2,500mg/kg. Excessive nitrate has been blamed by some experts for causing stomach cancer, although scientific opinion remains divided.

Trading standards officers found traces of pork in a 500g pack of Tesco frozen lamb mince. “The sample . . . gave a positive response for lamb and pork,” states the laboratory report.

A spokesman for Tesco said yesterday this was an isolated incident. “Our regular testing programme would have highlighted if there was an issue with this product,” he said.

A chicken “baton” sandwich contained 57% more salt than stated on its label. It was saltier than sea water.

“You might think you are eating a product which has a limited amount of salt,” said ProfessorGraham MacGregor, chairman of Consensus Action on FoodSalt and Health, a dietary campaign group, “but in the case of the chicken sandwich it has almost 60% more than is being declared.

“This is a serious issue Raised blood pressure is a major cause of strokes, heart attacks and heart failure and a major factor putting up our blood pressure is our salt intake. Obviously, there are fluctuations of ingredients in products, but these sound more than just fluctuations.”

Tests on a “controlled sodium” Tesco Kids Pizza — part of the same child-targeted range as the Breakfast boulders — revealed 0.37g of sodium per 100g. “The stated level of sodium in this product was 10 times that which would qualify as a reduced sodium food,” stated the laboratory report.

The Food Standards Agency has strict rules on the use of words “reduced” and “low”; but there is no definition of “controlled”.

Tesco’s spokesman said “controlled” meant there was “less sugar and salt than in the standard product” of the same type. Ian Tokelove, of the Food Commission, which campaigns for healthier food, described the term as “absolutely meaningless”, however.

He added: “What the consumer wants is clear and accurate information. They’re not getting that at the moment.”

Tesco insisted: “All of the issues are being investigated thoroughly and if we find a problem we will act. We try hard to get things right for customers and on the whole we do, but occasionally things go wrong.”

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