The ban, which extends measures already in place for under-10s, will curb television adverts for food and drink products with high fat, salt and sugar content.

Specifically the new measures, agreed last year, will ban adverts for junk food and drink around all programmes of particular appeal to children under 16 years.

According to official data released in October half of all Britons will be obese in 25 years if current trends are not halted; furthermore, 86 percent of men will be overweight in 15 years and 70 percent of women in 20.

Some campaigners say the ban which came into force Monday does not go far enough, calling for a total ban on junk food ads after 9:00 pm.

"We need urgent action to help people, especially children, avoid the less healthy, less happy and, ultimately, shorter life that obesity leads to," said Richard Watts of the Children's Food Campaign.

Prime Minister Gordon Brown launched a new 100-million-pound (205-million-dollar, 145-million-euro) programme in October aiming to increase from two to five the number of hours of physical education in schools per week.

Some 2.3 million pounds has already been set aside in the last 10 years to increase the number of hours of sport in school.