The childhood obesity epidemic could be levelling off in affluent homes but rising among those from disadvantaged backgrounds, research suggests.
People who are less well off tend to be wary of health messages telling them what to do - regarding it as "nanny-statism", experts said.
They calculated that obesity levels among children are set to "increase considerably" overall by 2015, echoing trends seen in other research.
Last week, data on more than a million children, as part of the Government's National Child Measurement Programme, found almost one in four boys and more than one in five girls are overweight or obese at the start of their school life.
Another 35 per cent of boys and 31 per cent of girls in their last year of primary school also have weight problems, equating to almost one in three, the figures for England revealed.
They have hardly changed in the last few years, suggesting drives to cut obesity rates have not yet had an impact.
Today's study, published in the Journal of Epidemiology and Community Health, looked at a different dataset, taken from the Health Survey for England between 1995 and 2007.
Experts from University College London concluded that around one in 10 children will be obese by 2015.
They said the number of obese boys more than doubled between 1995 and 2007, from 3.1 per cent to 6.9 per cent, while among girls it rose from 5.2 per cent to 7.4 per cent.
In looking to the future, the experts said obesity rates will be 35 per cent to 50 per cent higher among boys from lower socio-economic backgrounds aged two to 10 than among those who are more affluent. Meanwhile, the rate will be 25 per cent to 35 per cent higher among girls.
The authors added that these rates are repeated in teenage boys aged 11 to 18, but are less pronounced among teenage girls.
They concluded: "If the trends in young obesity continue, the percentage and numbers of obese young people in England will increase considerably by 2015 and the existing obesity gap between manual and non-manual classes will widen further.
"This highlights the need for public health action to reverse recent trends and narrow social inequalities in health."
The widening socio-economic gap "may be partly due to difficulties to reach and communicate health messages to families from lower socio-economic groups," the authors suggested.
"Previous research shows higher socio-economic status groups tend to follow recommendations for health behaviours and respond more actively to health-related media messages than do those of lower socio-economic status.
"It is possible that the recent exponential increase in obesity and obesity-related (diet and physical activity) media messages has been received more positively by non-manual than by manual families.
"As lower socio-economic groups tend to be wary of measures and messages aimed at changing their lifestyle because they see these as 'nanny-statism' that erodes their autonomy, it is possible that policies targeting children's eating and physical activity habits have not have been perceived favourably by manual classes."
The experts said it may also be taking longer for obesity levels to stabilise among families of a lower socio-economic status than among more wealthy families.