The survey found 16 per cent of reception class youngsters in Wakefield were obese followed by 11.9 per cent of four and five-year-olds in Hull.

Nearly one in five – 19.7 per cent – of 10 to 11-year-olds in Hull were obese and 19.5 per cent of children the same age in Bradford.

Doctors last night warned that urgent action was needed to combat the rising tide in obesity.

Worrying projections suggest 33 per cent of boys aged two to 10 will be overweight or obese by 2010, the second worst of any region in England, while a massive 44 per cent of girls aged 11 to 15 will be overweight in two years – the worst in the country.

Overall 39 per cent of men in Yorkshire and 27 per cent of women will be obese by 2010 – the highest regional rates in the country following a trebling of the problem since the 1980s.

Only 32 per cent of 5.2 million people in Yorkshire are a healthy size compared to a national average of 40 per cent.

Overall an estimated 3,600 deaths each year are already being blamed on obesity in the region mainly due to heart disease, stroke, diabetes complications and cancer.

Rotherham GP Matt Capehorn, who is regional chairman of the National Obesity Forum, branded the scale of the problem among children "shocking".

Yorkshire's children did not yet have the worst problems in the country but he warned they soon would unless trends were reversed. He said parents were failing to act if their child was obese – which was a far more serious problem. We have normalised obesity. In a playground, you can see overweight or chubby children and it's normal.

"In the past a child like that would have stood out like a sore thumb so you can understand why parents don't realise when their child has a problem and don't know the consequences and the seriousness of that problem. Parents want the best for their children but they don't realise the health consequences of being obese or overweight."

A similar survey of children is being carried out this term. Parents will be told about the results although the extent of warnings they will receive about their child's weight remain unclear.

Dr Capehorn said from next year there would be no chance to opt out from the checks. At the moment parents can refuse to let their children be weighed and youngsters can opt out.

"In this case, I've no problem with the nanny state if we are allowing little children to make decisions when it comes to their health." He said findings suggested people were not eating more but they were doing much less exercise. Each overweight child needed an individual solution. Quite often they were not put on a weight-reducing diet but a better, balanced diet and more exercise could instead stabilise their weight as they grew.

Dr Capehorn said any parents worried about their child's weight should go to their GP.