Companies including Vimto and Britvic, the company behind Tango, have been criticised for targeting children at schools with adverts disguised as "educational material" – such as creating a poem in praise of a soft drink and promoting a bag of crisps as healthier than an apple.

A new report, called "Through the back door", argues that some food and drink companies are using curriculum packs to advertise their products to children at school.

The Children's Food Campaign report claims that two-thirds of the curriculum packs surveyed contained company logos, two-thirds contained promotions for a product and two-thirds contained misinformation.

CFC, a lobby group for healthy food, highlighted a "blatant promotion" by Vimto, maker of the purple soft drink, where teachers in more than 1,000 schools were encouraged to use English lessons to promote the drink, at one time promoted by the animated Purple Ronnie character.

According to CFC, pupils were asked to write a poem in praise of Vimto for National Poetry Day.

The report found that the European Snack Association, backed by Pringles, KP and Walkers, compared the nutrient content of a 30g bag of crisps favourably with that of an apple.

"As you can see the bag of chips [crisps] provides from twice to thirty times as much of all the vitamins and minerals, three times as much energy, more fibre and complex carbohydrate," ran an extract selected by the CFC. "So how do you define a healthier food – one that is nutritionally inferior?"

Britvic, producer of soft drinks including Tango, used a picture on a chart of how soft drinks were made using "gooditives", not additives.

"We were flabbergasted by some of the claims in these packs," said the CFC co-ordinator, Richard Watts. "We found nutrition lesson plans about the benefits of eating crisps, claiming that colourings in fizzy drinks were to restore the fruit's natural colour, and telling children to only eat fruit and vegetables in moderation."

CFC has produced a list of the "top 10 dodgy claims" that it found were made by companies.

The claims included: children should not reduce food intake to lose weight, food colouring restores colour lost during processing, everybody should eat three portions of dairy products a day, some people with unhealthy diets should eat more cheese, and sugary food and drink products can be compared to bread, rice and pasta for carbohydrates.

CFC said that if these practices were tried in TV or print advertising they would be blocked, but marketing in schools is unregulated.

Commercial activity in schools is covered by guidelines produced by the Department for Children, Schools and Families and a code from the advertisers' body ISBA (Incorporated Society of British Advertisers).

The CFC, which says that UK companies spend £300m annually on advertising in schools, claims that these guidelines are "flouted with impunity".

The organisation claims that Magenta, a company that produces in-classroom advertising, offers a "captive audience of some 7.5m young people, their teachers, school managers, governors, parents and the wider community".

However, recent reports by Ofcom, the Advertising Standards Authority and the Department of Health have all found that so-called junk food marketing practices are mostly on the decrease.

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