Parents of fat children are being blamed by ministers for the failure of an attempt to measure the nation's childhood obesity crisis.

The results of a survey that was supposed to weigh and measure every reception class pupil suggested children are getting lighter. But data was distorted as not enough local health trusts did the tests and, where they did, parents of fat children refused to give permission for them to be weighed.

The Public Health minister, Caroline Flint, will be forced to admit to the shambles when she releases the National Childhood Obesity Database on Wednesday. She will say that in future, trusts will be formally required to carry out annual weighing and measuring of four- and five-year-olds, to build up a more accurate picture.