Child obesity levels have been rising for decades
A widening class gap is likely to be seen in the coming years in childhood obesity, a study suggests.
Previous research has suggested rates in England may be levelling off.
But the University College London team found this was happening most in children aged two to 10 from wealthier backgrounds.
Researchers said obesity rates among the lower classes were likely to be significantly higher by 2015 - for girls the levels may even be double.
They analysed data gathered by the government-funded Health Survey for England.
Currently 6.9% of boys and 7.4% of girls are obese - with the difference between the lower and higher classes 0.6% and 1.5% respectively for boys and girls.
But using historical trends, they predicted that by 2015 obesity rates could be above 10% for boys and 8.9% for girls.
Depending on the extent of the "levelling off" reported last month, the overall rates could be even lower.
However, it is the findings for social class that have shed even more light on the obesity problem.
The obesity rates for girls are likely to diverge from now on, the team said.
Among those from lower classes it is expected to keep rising to 11.2%, while for those from professional backgrounds it is likely to fall to 5.4%.
Among boys, both groups are likely to see a rise, but it will be faster in the lower class group, meaning 10.7% of this class boys will be obese compared with 7.9% of those from wealthier backgrounds.
Similar trends will also be seen in older aged children, the report in the Journal if Epidemiology and Community Health found.
Lead researcher Dr Emmanuel Stamatakis said: "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."
Tam Fry, of the National Obesity Forum, agreed awareness was more likely to be greater among wealthier families.
But he added: "It is also often quite expensive and time-consuming to buy healthy food and that puts wealthier parents at an advantage."
He said it was not clear why the differences were so marked in girls, although he said he suspected it was partly to do with the fact that boys tend to be more active generally.
The Department of Health said there was still more to do despite the levelling off which had been seen.
A spokesman said: "Obesity levels are still too high.
"We'll only turn the tide on obesity for good if everyone - government, families and industry - play their part."