Junk food ads during TV programmes targeted at under-16s will be banned, under rules put forward by regulators.
The restrictions focus on foods high in salt, fat and sugar
Ofcom says these foods include any that are high in fat, salt and sugar.
There will be a total ban on ads during children's programmes and on children's channels, as well as adult programmes watched by a large number of children.
Health bodies said Ofcom should have banned junk food ads before the 9pm watershed, but the food industry said the restrictions were "over the top".
Ofcom's measures will come into effect before the end of January 2007.
They are set to cost broadcasters an estimated £39 million in lost advertising revenue, Ofcom said.
The measures will apply to:
- All pre-school children's programmes
- All programmes on mainstream channels aimed at children
- All cable and satellite children's channels
- Programmes aimed at young people, such as music shows
- General entertainment programmes which would appeal to a "higher than average" number of under-16s.
The regulator has gone further than expected.
It had been considering a ban on junk food advertising during programmes aimed at under-nines. The extension to all shows aimed at under-16s will be subject to a brief consultation.
There will also be new rules governing advertising to primary school age children.
The use of celebrities and characters, such as cartoon heroes, free gifts and health or nutrition claims would be banned.
Ofcom suggests the package would mean that, in households where children's viewing includes a large number of programmes targeted at adults as well as those for children and young people, under-16s would see 41% fewer junk food ads.
A Food Standards Agency ratings system will be used to assess which foods are too high in fat, sugar and salt to be advertised to children.
Ed Richards, Ofcom chief executive, said: "Based on the evidence and analysis we believe the case for intervention is clear.
"We will introduce significant but proportionate measures to protect children under 16."
He added: "We will look to advertisers and broadcasters to follow both the spirit as well as the letter of the rules we are putting in place."
'Over the top'
But health campaigners criticised Ofcom's proposals.
Dr Vivienne Nathanson, Head of Science and Ethics at the British Medical Association, said: "Ofcom's ban does not go far enough. Some of the most popular programmes amongst the under-16s are soaps which will not be covered by this ban.
"We are in the midst of an obesity epidemic and must use all the weapons in our armoury to prevent the next generation of British children being the most obese and unhealthy in history.
"Ofcom clearly believes that TV advertising has an effect on children's eating habits, yet it does not have the courage to recommend a more comprehensive ban."
Paul Lincoln, chief executive of the National Heart Forum, said: "This represents a missed opportunity by Ofcom."
And Children's Commissioner Sir Al Aynsley-Green said: "In practice, the status quo will barely shift, with no advertising restrictions for programmes such as X-Factor and Coronation Street - unless it can be proved that 20% more children than adults are watching."
However Melanie Leech, director of the Food and Drink Federation said Ofcom's regulations were "over the top".
She added: "We are shocked that after a lengthy consultation Ofcom has moved the goalposts.
"This issue has always been about advertising to young children and industry responded on that basis with a package of strong measures designed to meet the government's objective."
And David Lynn, of children's channel Nickleodeon, said: "There's no doubt that the restrictions announced today very tough and that they are going to impact the quality of kids' programming in the UK.
"They amount for a total ban on advertising for dedicated children's channels."
A spokesman for the Treasury said: "The Chancellor welcomes Ofcom's report and their proposals to tighten the restrictions on the advertising of unhealthy foods during programmes that children watch."
Gordon Brown, Health Secretary Patricia Hewitt and Culture Secretary Tessa Jowell are to host a seminar at 11 Downing Street to hear the views of parents and consumer groups and to consider what more could be done to improve child health.