Researchers have found that 20 per cent of 14 year olds in the UK are obese.
More than one in three British teenagers are overweight or obese, a study has found.
Researchers have found that 20 per cent of 14 year olds in the UK are obese and a further 15 per cent are overweight.
Leading children's doctors say the study is further evidence of the "childhood obesity crisis" gripping Britain.
The new figures come from research conducted by experts at the Centre for Longitudinal Studies at University College London (UCL).
Researchers from UCL's Institute of Education examined data from more than 10,000 teenagers who are taking part in the Millennium Cohort Study - a study tracking the lives of thousands of youngsters born at the turn of the century.
They found varying responses from across the UK - 40 per cent of 14 year olds in Northern Ireland were overweight or obese compared to 38 per cent in Wales and 35 per cent in both Scotland and England.
Youngsters whose mothers had a low level of education were more likely to be of excess weight than those whose mothers had a degree.
The authors also found differences between white and black teenagers - with 48 per cent of young black people classified as having excess weight, compared to 34.5 per cent of white adolescents.
Professor Emla Fitzsimons, co-author of the study, said: "Children who are overweight or obese face an increased risk of many health problems later in life, including cardiovascular disease and type 2 diabetes.
"Overweight and obesity are also associated with psychological problems such as low self-esteem and depression, and with lower educational attainment.
"As members of the millennium generation reach early adolescence, rates of obesity and overweight remain a public health concern."