The extent of Britain’s obesity crisis is being exaggerated, according to research.

The Social Issues Research Centre (SIRC), an independent think-tank, said that ministers and some health lobbyists are using an out-dated system to calculate obesity.

While the ‘national standard’ used by the Government to calculate obesity suggests that more than 15% of all children are obese, the research found that the ‘international standard’, which also compares body mass and height but includes a broader sample, suggested that fewer than 7% of children were dangerously overweight.

Peter Marsh, co-director of the SIRC, said a study of body mass index data showed that the average weight of girls and boys aged under 16 had increased by just half a kilo over the past decade, reported The Times today.

David Haslam, chairman of the National Obesity Forum, is reported to have described the SIRC report as unhelpful when, he said, it was widely acknowledged that action was needed on childhood obesity.