The UK advertising watchdog has ruled that McDonald’s Happy Meals can be advertised during children’s TV shows because they are “healthy”, but banned ads for KFC and Kellogg’s Coco Pops for promoting junk food to young people.

McDonald’s has strived to improve the nutritional value of Happy Meals by making cheeseburgers available only on request, reducing the serving size of fries that come with Chicken McNuggets and cutting the sugar in chocolate milk, but health campaigners still see the home of the Big Mac as the frontline in the fight against junk food advertising.

The Advertising Standards Authority dismissed a complaint that a Pokémon-themed Happy Meal ad, which featured products including Chicken McNuggets, should not have been allowed to run between episodes of Peppa Pig.

Under UK rules, children cannot be targeted with adverts for products that are high in fat, salt and sugar, and licensed characters should not be used to promote such products to them.

“We noted that 80% of mains, 100% of sides and 64% of drink options available in the Happy Meal were non-HFSS [junk food] products,” said the ASA, which cleared McDonald’s to continue advertising Happy Meals to children. “We therefore considered that the Happy Meal was, overall, a non-HFSS product combination.”

While customers can order products such as cheeseburgers, Coca-Cola and milkshakes with Happy Meals, McDonald’s does not feature them in its advertising, so it can comply with UK laws regarding targeting junk food ads at children. The company said it had not advertised that cheeseburgers are part of the Happy Meal range for more than a decade in the UK.

A spokeswoman for McDonald’s defended its advertising strategy. “We comply and go beyond the UK’s stringent regulations on marketing to children and use our marketing to help families understand more about the range of food options we offer,” she said.

While McDonald’s avoided a ban, the ASA ruled that a Kellogg’s Coco Pops ad for a granola product, which appeared between episodes of the Mr Bean cartoon, broke the UK advertising code. While the ASA deemed that the granola product itself was not junk food, the wider content of the ad broke UK law.

The advert featured the Coco Pops monkey and focused on making the cereal “chocolatey” – a hallmark of the wider Coco Pops range, which is deemed to be too sugary to market to children – and not enough on the healthier granola. The ASA banned the ad.

Caroline Cerny, of the Obesity Health Alliance, which lodged the Coco Pops complaint, said: “This is just another example of the ever-evolving tricks brands use to get their products in front of children, and why we need stronger regulatory protection online and a 9pm watershed on junk food adverts on TV.”

The watchdog also banned a poster for KFC’s Mars Krushems drink for appearing on a phone box near the entrance to a primary school, which is not allowed. KFC said the ad was placed there in error.

Later this year the government is launching a consultation on junk food marketing restrictions in an attempt to tackle the growing childhood obesity problem.

The consultation will look at measures including two-for-one junk food deals and the sale of sweets and chocolates around supermarket checkouts, as well as the potential for a pre-9pm ban on junk food ads.

Barbara Crowther, the coordinator of the Children’s Food Campaign, said: “Clear guidance about what constitutes a HFSS advert and a stronger legislative framework to restrict junk food marketing are needed if we are to adequately protect children from obesity.”