EVERYBODY tells “good lies” in their private life, whether about Santa Claus or how nice that new haircut looks. We understand what Mark Twain meant in describing how Tom Sawyer’s God-fearing auntie, suspecting he had lied to comfort her, “fortified herself with the thought: ‘It’s a good lie – it’s a good lie – I won’t let it grieve me.’ ” But public life is a different matter. We now know that we were misled by those horror stories about a three-year-old girl who died of heart failure. She weighed six stone, not because her parents stuffed her face with food, but because of a rare genetic condition. Her bereaved family has been traumatised, and other parents guilt-tripped about the mortal dangers of overfeeding our children, on the basis of junk facts.

Yet defenders of the Commons health service committee report that highlighted this little girl’s death now seem to ask whether this really matters. Overblown concerns about one example, they suggest, should not distract from the “broader truth” of the report’s message about the need for drastic action to combat child obesity. But it does matter that the headline-grabbing example in such an influential report misled us all. It matters that elected representatives, experts and journalists are held to account for their evidence. There can be no licence to publish dodgy facts by claiming that they serve a worthy cause.

The MPs now predictably blame the press for misreporting the cause of her death. Even if that were true, it would not explain why the committee allowed the scurrilous headlines to go uncorrected until last week, when Brendan O’Neill broke the true story about the girl’s condition in spiked, the online magazine that I edit. Disingenuously, David Hinchliffe, the Labour MP who chairs the health committee, responded that its obesity report did not say or imply that the girl died of overeating.

What other conclusion did he expect people to draw? Her shocking death appears in the second paragraph of a report that demands a ban on junk food advertisements and absurdly calls for yearly “weigh-ins” for school pupils.

There is no mention of rare genetic conditions. When it was published, Hinchcliffe seemed clear that her death should be read as a warning of what could happen to other three-year-olds: “It was the first situation of its kind we had come across, but we feel it may become a more serious consequence of obesity in the future.”

The committee’s defenders insist that this misrepresentation should not be allowed, as the chairman of the National Obesity Forum puts it, to “distract attention from the root point” in the report. He says that the girl’s story “was used to gain a bit of drama and it certainly worked, but in retrospect it should probably not have been used”.

In other words, the ruse would have been all right if it hadn’t been found out. Since when has politically scripted melodrama had any place in the discussion of children’s health? This case fits into a pattern of public figures playing fast and loose with the facts, and seeking to justify it by talking about the “greater truth”. Think of the Government’s “dodgy dossiers” on Iraq. New Labour spokesmen might concede that they got the odd detail wrong about Saddam’s weapons of mass destruction, but insist that what matters is that the war was just.

Opponents of the war have used similarly contorted arguments. According to one senior lecturer in media law, even if the Daily Mirror’s photos of British soldiers torturing Iraqi prisoners were fakes, what really matters is that “the facts remain the same” about the abuse that they claimed to depict.

Not so long ago, the claim that a war was right even if its justification was wrong, or that a fake was the same as a fact, would have been considered the province of Dr Goebbels. I realised how things were changing a few years back when one pillar of the liberal media openly praised the “good lie” in the Tory Government’s Aids campaign, which exaggerated the threat of a heterosexual epidemic to scare people into changing their sexual behaviour. Today, more people who should know better sound like Tom Sawyer’s auntie defending a “good lie” in public life.

“Good lies” make for badly informed policy. You cannot justify bad journalism by claiming it is for a good cause. And the pursuit of a “greater truth” is no excuse for twisting the facts about a child’s death. Instead of simplistic, black-and-white dramas, we need serious debate about such complex issues as child obesity or Iraq.

There is no time to lose. As Twain also reminds us: “ A good lie will have travelled half way around the world while the truth is putting her boots on.”

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