The rules restrict the advertising of unhealthy foods
Adverts for unhealthy foods are still appearing during TV programmes seen by children, despite curbs introduced in January, a consumer watchdog has said.
Which? said the five programmes with the most child viewers and only four of the top 20 most popular children's shows were covered by Ofcom's rules.
These state that ads for "less healthy” foods are not allowed in or around programmes which "appeal" to under-16s.
But advertisers said Which's list included shows "not aimed" at children.
A programme is defined as being of particular appeal to children if the proportion of those under 16 watching a programme is 20% higher than the general viewing population.
This means shows like The Simpsons and SpongeBob SquarePants are covered, while shows like Beat the Star, Animals Do The Funniest Things and Emmerdale are not, even though they are watched by thousands more children.
A two-week analysis by Which? found that ads for products including Coca-Cola, Oreos and Kellogg's Coco Pops were broadcast during programmes popular with children but not covered by the restrictions.
It said ITV's Beat the Star attracted more than half a million child viewers during the monitoring period, but had contained ads for Coca-Cola, Dairylea Dunkers, Nachos and Sprite.
Which? food campaigner Clare Corbett said: "The ad restrictions may look good on paper but the reality is that the programmes most popular with children are slipping through the net.
"If these rules are going to be effective, then they have to apply to the programmes that children watch in the greatest numbers."
She added: "We're not anti-advertising, we're just against the fact that most of the ads children see are for unhealthy products, rather than the healthier foods they should be eating more of."
But the Advertising Association said Which? seemed to want to unfairly restrict companies' ability to deliver commercial messages.
Chief executive Baroness Peta Buscombe called its report "sensationalist, unconstructive and missing the point" and said the advertising industry took a "responsible approach" to food advertising.
She added: "Their list includes programmes clearly not aimed at children and films screened after 10pm.
"There clearly has to be an element of parental responsibility on which programmes they allow their children to view."
A Department for Culture, Media and Sport spokesman said: "For the first time, TV adverts for foods high in fat, salt and sugar are banned during programmes aimed at or of particular appeal to children under 16.
"Although children still see some of these advertisements, the current Ofcom regulations mean that the viewing of these adverts by children is reduced by an estimated 50%, an impressive amount."
He added: "We appreciate that there are calls for further restrictions on UK TV advertising but these should be considered once we have had a chance to assess the impact of current measures."
Ofcom is set to report to government on the success of its restrictions in December.
The Food Standards Agency, which drew up a model for deciding if a food was unhealthy, is also to assess how well it is performing.