The findings also condemn the call by Tessa Jowell, the culture secretary, for agencies to use their creative skills to promote healthy products, saying it was "rather naive" and "an idealistic and ill-thought-through notion".
"Advertising agencies are commercial businesses and can not be expected proactively to fund the large-scale promotion of healthy foods for the public good," the report said.
"They will clearly be able to put their 'creative genius' to good ends if they are commissioned to do so, which raises the question of who might reasonably be expected to provide such funding."
A year-long inquiry by the Commons Health Select Committee urged food companies to head off the ban by voluntarily withdrawing such ads. John Reid, the health secretary, is increasingly in favour of a ban but may adopt the MPs' "final warning" proposal when he publishes a White Paper this summer.
The Labour MP-dominated committee's report on the obesity crisis facing Britain, published Thursday May 27, stops short of advocating a total ban on all ads for unhealthy foods, warning that if TV commercials were outlawed, "the marketing effort would simply be diverted to other areas" such as internet or point-of-sale promotion.
The MPs were "disturbed by the ineffectiveness of the Advertising Standards Authority" and proposed that Ofcom reviews its role. They added it was not the first time they had found the ASA's performance "disappointing".
The committee called for a massive government-funded education campaign on healthy eating and exercise, a move likely to be supported by ministers.
But it admitted the drive would still be dwarfed by the ad budgets of multinational food and drink companies.
MPs urged Jowell to review the marketing of unhealthy products and the role of sports stars such as David Beckham and Gary Lineker in their commercials. "Assuming the food and advertising industry is genuine in its desire to be part of the solution, a starting point for this would be for companies to agree clear public health targets," they said.
The report puts huge pressure on the government and Ofcom to tighten the code on food and drink ads, which will be reviewed by this summer.
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