Junk food TV advertising targeting children has dropped by a third since stricter regulation aimed at tackling obesity was introduced, media regulator Ofcom claimed today.

Ofcom began a phased introduction of tighter restrictions on junk food TV ads from April last year, with a ban on junk food advertising around all children's shows and programmes that have a "particular appeal" to under 16s.

The regulator estimates that the volume of junk food TV ads seen by children aged four to 15 across all hours dropped by 34% in the 12 months since last July, compared with the 2005 calender year, before restrictions were introduced.

However, there has been a 22% increase in the use of celebrities in junk food TV ads. Ofcom pointed out that many of the TV ads using celebrities are likely to appeal "mainly to adults", citing William Shatner and Ian Botham as examples, and the growth seen "all took place in adult airtime".

The media regulator said today that it expects the amount of junk food TV ads – for products that are high in fat, salt or sugar – seen by children to decline even more when the ban extends to all children's channels from January 1.

For younger children aged between four and nine, the estimated reduction was 39%, and for older children, aged 10 to 15, slightly less, at 28%. Overall the amount of junk food TV ads aired between 6pm and 9pm has fallen by 29%.

Ofcom's review also found that while children's channels saw a decline in food and drink advertising revenue, this has been "more than offset" by a growth in other sectors.

The main commercial networks – ITV1, GMTV, Channel 4 and Channel Five – saw an overall reduction in advertising revenues and a 6% decline in income from food and drink commercials.

Ofcom said that "most other" digital commercial channels increased their revenue from food and drink advertising over the review period.

The review also found that children are seeing 69% less food and drink advertising using licensed characters, such as figures from cartoons and films.

Ofcom said there had been a 36% reduction in ads using "brand equity characters" specially created for ads, such as Kellogg's Tony the Tiger, and a 36% reduction in commercials enticing younger viewers with free gift offers. Junk food ads making health claims have dropped by 18%.

Overall, children saw 41% less advertising overall on the main commercial channels – ITV, Channel 4 and Channel Five – and 27% less advertising on digital commercial channels, according to the regulator.

However, there was a 7% increase in junk food ads on digital commercial TV channels. The biggest increase occurred on the digital spin-off channels of the main commerical broadcasters – such as ITV2, E4 and Five US – which saw their share of junk food ads targeting children grow from 4% to 16%, because of the decrease on the main commercial networks.

Ofcom estimates that about 40% of all food and drink TV ads that are seen by children were for junk food products that are likely to appeal to them.

The regulator added that it appeared advertisers were not seeking loopholes in the restrictions to continue to market to children.

"In relation to brand advertising and sponsorship, there is no evidence which supports the view that advertisers are using these techniques to circumvent the restrictions on HFSS advertising, although the paucity of data makes definitive conclusions impossible," said Ofcom.

The media regulator said that once all TV ad restrictions are implemented – including the total ban from 1 January on junk food commercials on kids' channels – the volume seen by children is likely to reduce by 41% of the level seen in 2005.

Ofcom said that it will launch another review of the TV junk food regulations in 2010, when the media regulator will have access to full-year data for this year and 2009.

The findings, while not a huge surprise, will provide ammunition for advertisers who have been fighting to avoid more draconian restrictions, most notably a pre-9pm watershed ban on junk food advertising.

Ofcom's review is backed by the findings of a compliance report into junk food advertising by the Advertising Standards Authority published earlier this month that showed that advertisers were sticking to the new rules.

In October, the Department of Health published its own report into junk food advertising, which found that "child-themed ads" across all media fell 41% between 2003 and 2007.

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