Which? has renewed its bid for a 9pm watershed on junk food ads after new research has shown that half of the top programmes watched by children are not covered by existing rules.
This year's restrictions banned adverts for high fat, salt or sugar foods from being shown in or around programmes aimed at under 10s.
Yet the rules, introduced in April, were based on the proportion of young viewers rather than the actual number.
Which? says this means that adverts promoting unhealthy foods are not allowed during The Simpsons, with a child audience of 163,200 but are allowed during The X Factor, which has nearly three times the child audience.
Which? analyses of advertising during programmes found that those with the most child viewers advertised sugar rich products such as Mars Planets, Kinder Bueno and Smarties.
Which? food campaigner Miranda Watson said: "This research shows that unhealthy foods are being advertised during the programmes with the highest number of child viewers. The only way to shield children from TV ads for unhealthy foods is a 9pm watershed.
"There is no silver bullet in the fight against obesity but tougher restrictions on the way unhealthy foods are marketed to children will play an important role in helping parents to instill healthy eating habits in their children."