A total ban on adverts for unhealthy food and drink products around TV programmes for under-16s has come into force.
It extends similar restrictions already in place for shows aimed at children under 10 years old.
The new curbs affect commercials for food and drink products high in fat, salt and sugar.
The measures were developed by the communications regulator Ofcom in response to rising levels of childhood obesity in the UK.
Adverts around youth-oriented and adult programmes which attract a significantly higher than average proportion of viewers under-16 will also be affected, Ofcom said.
Children's TV channels will be allowed to phase in the full ban by the end of December 2008.
Ofcom drew up the new advertising restrictions following a public consultation which drew fierce debate from opposing camps.
Health and consumer groups are still lobbying for a pre-9pm ban on all TV adverts for foods high in fat, salt and sugar. They argue that many television shows popular with young viewers - such as early evening soaps - slip through the net because they also attract a large proportion of adult viewers.
But an Advertising Association report released in October said the number of TV adverts for food, drink and fast-food restaurants watched by four to nine-year-olds was already down by more than 25% compared to 2006.
Ofcom will review the effectiveness of the new advertising restrictions in autumn 2008. Food Standards Agency guidelines are used to decide which food and drinks products are subject to the curbs.
