Cartoon characters such as Tony the Tiger that promote foods high in salt, fat and sugar are disappearing from TV but appearing more frequently in press, radio and the internet, prompting the government to warn it will "keep an eye" on advertising.

Companies targeting children with "junk food" ads have significantly cleaned up their act over the past five years, according to a government report by the Department of Health, revealed exclusively today by MediaGuardian.co.uk.

Child-themed food advertising across all media fell 41% between 2003 and 2007.

The government said the report will be of critical importance in measuring the impact of advertising as its battles against childhood obesity.

In 2003, companies spent £103m on food advertising to children, which included using licensed characters, film tie-ups, free toys or a link to a children's TV programme, the report found.

By 2007, that figure had fallen by 41% to £61m.

The drop was most notable in TV advertising, as companies cleaned up their marketing policies and Ofcom moved to introduce regulations last year to protect children from junk food ads.

The report showed a 46% decrease in junk food TV ads targeting kids in the last five years, from nearly £100m in 2003 to about £55m last year.

However, advertisers increased child-themed press adverts by 42%. And food adverts aimed at children across radio, the internet and cinema advertising rose 11% over the same period.

"I am pleased that there are now fewer ads on TV that are tempting our children into bad eating habits," said the public health minister, Dawn Primarolo.

"But we must keep our eye on other types of media. I hope the industry will continue to play its part in reducing the exposure that children have to the promotion of food which is high in fat, salt or sugar".

Between 2003 and 2007, according to the study, there had been 71% decrease in fast food promotion, a 62% decrease for confectionery ads, a 52% drop for non-alcoholic drinks and a 37% drop for cereal.

The report, which comes as Ofcom conducts a review of junk food TV advertising rules, forms part of a wider governmental strategy, under the banner "healthy weight, healthy lives" including a three-year, £75m anti-obesity campaign due to start in January.

The governmental findings will provide the industry with ammunition following two reports put out in recent weeks by consumer body Which? criticising Ofcom's advertising restrictions and the tactics of advertisers.

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