Take a cursory look at the TV schedules and you will find they are littered with programmes that uncritically regurgitate government messages on public health. Scaremongering about the supposed obesity epidemic, while challenged by many researchers as over-hyped, is accepted as a given in programmes such as Supersize Kids on Channel 4, Fat Families on ITV or Chubby Children on Living TV.

But the doyen of all of them is St Jamie Oliver. The DoH must adore him. I rather agreed with Boris Johnson’s swipe at the TV chef. I also cheered when a couple of mums from Rotherham rebelled and told Salad Boy to stop telling the nation’s children (and their parents) what not to eat.

The great and the good of politics, however, flocked to Jamie’s defence. Perhaps one reason why a TV pundit seems to have become such an untouchable Messiah is because he — and a new breed of lifestyle “experts” — have become the saleable face of “health correctness” and the unwitting popularisers of the nanny state.

You can see why politicians enjoy the prospect of outsourcing their policy messages to TV presenters. Arguments that, when presented by politicians, might be unappetising become pukka when pushed by a trendy campaigning chef. Ms Flint could not get away with deriding ordinary parents as “f***ing tossers”, even though this is the implicit message behind so many of new Labour’s health promotion initiatives.

But while all governments use whatever means necessary to get their policy priorities into the nation’s living rooms, broadcasters seem blind to the way their programmes mesh with Government propaganda. The BBC’s recent Fat Nation, a “fully integrated pan-platform campaign” across television, radio and online services, admitted that, although “the nation is bombarded by messages . . . from the Government”, too many individuals have concluded that the obesity warnings do not affect them personally. Therefore Fat Nation offered to help, presenting itself as a “motivational service” aiming “to provide guidance and raise the nation’s awareness of the issues; to change attitudes of people . . . and to motivate them to change their behaviour through diet and exercise over an extended period”.

In the commercial sector, the Government regulator, Ofcom, now run by Tony Blair’s former media adviser, Ed Richards, is threatening draconian bans on advertisements for “junk food” aimed at children. This is despite Ofcom’s own research indicating that such advertisements have only a “modest direct effect on children’s food choice”. Ironically, while there is no shortage of programmes about unhealthy kids, according to the TV industry’s campaign Save Kids TV, the ban means that fewer programmes will be made for children because of the loss of income from advertising. Apparently children’s creative undernourishment is unimportant as long as they get the right messages about fatty foods.

While there is a fashionable queasiness about the big bad corporations influencing children to adopt unhealthy lifestyles, there is little queasiness about TV delivering the Government’s messages. Celebrity endorsements of crisps, cola and sugary food by the likes of Gary Lineker are denounced as a shocking manipulation of children’s minds. But somehow it is not shockingly manipulative when the Food Standards Agency advocates that broadcasters use — guess what — celebrities and cartoon characters to sell children 5 A DAY (five portions of fruit or vegetables a day) messages.

BBC Worldwide uses CBBC characters such as the Teletubbies and the Frimbles to brand food products deemed nutritionally sound. It appears that Ofcom’s problem is not about using cartoon characters or celebrities to influence children’s diet or lifestyle per se. Rather, if they are to be used, they have to endorse the right diet and lifestyle. And what is “right” is increasingly dictated by the State.

Policy placement threatens journalistic integrity and political accountability. When policy issues are the focus of current affairs programmes, the journalists must adhere to strict guidelines of veracity. The Paxmans and Snows keep a rein on the wilder claims of politicians. Such stringent broadcasting criteria do not apply when policy messages are delivered through entertainment formats. Kris Murrin, presenter of the misanthropic Honey We’re Killing the Kids, can get away with terrifying hapless parents into believing they are poisoning their offspring by letting them munch on a bag of crisps, without any cross-examination of her “facts”. Where is the evidence to back up Sainsbury’s poster boy’s litany of ill-founded contemporary prejudices against modern food? Shouldn’t St Jamie be challenged to explain how our digestive systems distinguish between the nutritional content of ciabatta with a drizzle of olive oil versus bread and dripping?

Policy placement is not just about diet. Just when Tony Blair focuses the domestic agenda on “the politics of behaviour”, we have a flurry of reality TV shows about changing people’s behaviour. The message is that private lives need mentoring and monitoring by third party “experts”. The TV equivalent of the Government’s Sure Start and Every Child Matters policies include Nanny 911 or Supernanny. As for the preoccupation with yobbish behaviour, Channel 4 has commissioned both Mind Your Manners and The Nightmares Next Door.

As Boris Johnson has found to his cost, challenging orthodoxies can get you into trouble. But it’s time to drag the politicians out from behind the celebrity TV stars and hold both to account for the policies they peddle.

Claire Fox is director of the Institute of Ideas