More than a third of children about to leave primary school are obese or overweight and the numbers are rising, according to official figures from the school measurement programme.

More than 1 million children were weighed and measured during the 2011/12 school year in the reception class and in year 6, the last year before they move to secondary school.

Over a fifth (22.6%) of the youngest children, just starting primary school, are either overweight or obese, the data from the National Obesity Observatory shows. But by the time they have reached the last year of primary school that figure has risen to one in three (33.9%).

The new figures suggest there has been little progress in the drive to keep children's weight down in spite of major concerns. There has been a small increase in year 6 from last year, when 33.4% of pupils were obese or overweight. The proportion in reception class is unchanged.

The leader of the UK's specialist children's doctors said parents needed more help ensuring their children ate healthily and took enough exercise, such as by a crackdown on the advertisement of foods high in fat, salt or sugar before the 9pm television watershed.

"We know that the environment in which our children grow up is conducive to eating too much of the wrong sorts of food and a sedentary lifestyle. So in order to get children on the right track early on, we need to be looking not only at the parents' role in encouraging active lifestyles and providing healthy food for their children, but also how society can support them in doing so.

"That includes looking at factors such as how cooking is taught in schools, ensuring school meals are nutritious, that healthy food is affordable to everyone and that children's exposure to junk food advertising is limited," said Dr Hilary Cass, the president of the Royal College of Paediatrics and Child Health.

The government said it was already taking action to encourage families to eat a healthy diet, referring to its much-criticised agreements with supermarkets and the food industry on what is put on sale as well as its Change4Life social marketing campaign.

"Through the responsibility deal, major supermarkets and retailers are working together to cut calories," said public health minister Anna Soubry. "But we need to maintain and build on this. Soon we will see more fruit and veg added to ready meals, and supermarket fruit and veg sections will be expanded.

"As part of Change4Life, we have run a number of initiatives to get children up and active, and in the new year we will be launching a new campaign to encourage healthy eating."

The figures show more boys are overweight or obese than girls and there is a marked social and economic divide. Obesity was most prevalent in the most deprived areas. It was also highest among black children and lowest for Chinese. Obesity was higher in urban areas than in rural areas for both age groups. The strategic health authority for the London area had the highest obesity prevalence for both reception and year 6. The lowest rates in year 6 were found in the south-central area and the lowest rates in reception classes were on the south-east coast.