Children who watch just 20 television adverts a week for sugary breakfast cereals eat a staggering 30 per cent more of them than children who see none, shocking new research has revealed.
Parents and health experts have long been concerned about the impact of repeated adverts for cereal and other high-sugar foods on youngsters' eating habits.
Now research has uncovered the startling scale of the relationship between the number of ads seen by youngsters and the amount of the breakfast products they consumed as a result.
Scientists found that for every ten cereal commercials a child under the age of five watched weekly, their consumption of the products jumped by almost 15 per cent.
And young children viewing 20 cereal adverts per week would consume nearly 30 per cent more of these cereals than those who didn't watch the commercials.
Health campaigners said the research proved beyond doubt that adverts for sugary breakfast cereals were helping to fuel Britain's child obesity crisis.
It will also fuel criticism of the Government's recent decision not to extend the 'sugar tax' on fizzy drinks to cover other products. Tam Fry, of the National Obesity Forum, said last night: "We need a sugar tax on cereals and a blanket ban on advertising these products to children."
Professor Graham MacGregor, chairman of the pressure group Action on Sugar, said: "There's no doubt that sugary cereals are one of the reasons so many children are becoming obese, with some now developing type two diabetes in adolescence."
And TV chef Jamie Oliver, who lobbied strongly for the sugar tax and is now backing the Sugar Smart campaign aimed at reducing sugar consumption across all ages, said: "We're facing a growing crisis where one in four children are leaving school either overweight or obese, seriously increasing their chances of developing diet-related diseases earlier in adult life."
One in five children entering primary school is now overweight or obese, according to official Government figures.
The average child under ten now consumes 14 teaspoons' worth of sugar daily, according to Public Health England. That's more than twice the six teaspoons that an adult should limit themselves to daily, under recommendations from the World Health Organisation.
Some cereals are more than a third sugar - meaning a 30g bowl can contain about three teaspoons' worth.
Experts say the latest study proves TV advertising has a powerful effect on children's eating habits. It was carried out by researchers from the Geisel School of Medicine at Dartmouth University in the US, who found more than 40 per cent of children were exposed to television adverts for high sugar breakfast cereals on a regular basis.
Writing in the journal Appetite, the researchers concluded: "These findings support recommendations to limit the marketing of high-sugar foods to young children. Ample evidence suggests cereals most heavily advertised to children are the least nutritious and contain the greatest amounts of added sugars."
In August, the Government unveiled its long-awaiting childhood obesity strategy. Although it included a 'sugar tax' on the soft-drinks industry, it was not extended to other products.
In the UK, food manufacturers are banned from showing adverts for unhealthy foods during children's television programmes.
But many children still see commercials for sugary foods at other times. A spokesman for the Food and Drink Federation said the sugar tax would make "no significant difference" to the obesity crisis.
He said: "Since 2009, the advertising of all products high in fat, salt or sugar has been banned from children's programmes and the Federation and its members support the extension of that ban to non-broadcast media, including online.
"The causes of the obesity challenge we face in this country are far more complicated than any single ingredient, food or drink."