The government has been accused of performing a u-turn on banning junk food in schools, after the culture secretary questioned the value of a ban on advertising.

Writing in the New Statesman, Tessa Jowell said: "I could say, in response to a populist campaign, that we'll take those adverts off the screen, only to find that it makes not a blind bit of difference to childhood obesity and diets, but that ITV can no longer afford children's programming."

Ministers have said in the past that such ads would be banned if the food industry could not stick by a voluntary code.