Britain is starting to overtake America in obesity rates, with the latest figures showing that more children in England are classed as obese at the age of 11 than in the US.

The proportion of US children aged 9 to 11 who are obese is 18.5%. The figure for children in their final year of primary school in England is at a record high of 20%.

Secondary-school children are also more obese. In the Health Survey for England, 23% of children aged 11 to 15 were obese in 2016. In America, 20.6% of children aged 12 to 15 were obese.

Simon Capewell, a professor in public health and policy at Liverpool University, said: 'Our worst fears have come to pass. We have completely adopted the American lifestyle with the inevitable consequences. The government needs to stand up for our children.

The proportion of US children aged 9 to 11 who are obese is 18.5% while those n in their final year of primary school in England is at a record high of 20%.

'We have an obesity epidemic in children and this translates into an epidemic of disease in adults of diabetes, heart disease, stroke, common cancers and mental health problems. This is a preventable catastrophe.'

The Organisation for Economic Co-operation and Development (OECD) reports that UK adult obesity rates rose from 14% to 26.9%, between 1991 and 2015, an increase of 92%. This compares with an increase in obesity rates from 23.2% in 1991 to 38.2% in 2014, a rise of 65%, in America.

The US is the most obese nation of the 34 OECD countries and still has higher childhood obesity rates than the UK. However, the disclosure that a greater proportion of 11-year-olds in England are obese will put Theresa May under renewed pressure to clamp down on junk food marketing.

May is to unveil a new anti-obesity strategy within weeks. The mayor of London, Sadiq Khan, announced this month that he plans to ban ads for foods high in salt, fat and sugar from the capital's Tube and bus network.

A government report has warned that obesity rates are likely to rise from a quarter of adults to half by 2050, costing the NHS about £10bn a year. The wider economic costs are put at £50bn annually.

Children in state schools in England have weight and height measured in reception year, aged four to five, and year 6, aged 10 to 11. The data is submitted to NHS Digital.

Wales only measures reception children, with 14.5% found to be overweight and a further 11.7% obese. Scotland records weight and height in first year of primary when 12% of children are at risk of being overweight and 10% at risk of being obese.

The most recent NHS data, for 2016-17, shows that nearly a quarter of reception children in England were overweight or obese. In year 6, it was over a third. The proportion of children in reception classified as obese stood at 9.6%. The proportion who were obese in year 6 rose from 18.3% in 2007-8 to 20% in 2016-17.

Areas with the highest rates of child obesity include Barking and Dagenham in east London at 29.2%, Sandwell in the West Midlands at 27.8% and Copeland in Cumbria at 25.1%.

Separate data from the Health Survey for England shows the proportion aged 11 to 15 who are obese rose from 19% in 2007 to 23% in 2016.

In America, the data is gathered by the National Health and Nutrition Examination Survey. It uses a different benchmark, but the figures show a smaller proportion of children are classified as obese.

Tam Fry, chairman of the National Obesity Forum, a health campaign group, said: ' We need far more radical policies with a complete ban on advertising fatty and sugary foods.'

The Department of Health said: 'We know child obesity is one of our greatest public health challenges. That's why our obesity plan goes further than any other country. Our soft drinks industry levy has removed [large amounts] of sugar from children's diets.'