Gordon Brown has announced extra cash for school sports in a bid to tackle the growing problem of childhood obesity.

Speaking on a visit to a school in south London, the prime minister said that although the government has invested £2.3bn in physical education over the last 10 years, more needs to be done.

Brown announced an extra £100m this year to try to broaden the range of sports available to children as a new survey revealed a worrying predicted rise in levels of obesity in the UK.

It suggested that 86 per cent of men will be obese in 15 years' time, and 70 per cent of women will be obese in 20 years' time.

The prime minister said more needed to be done on food labelling to help parents make the right decisions for their children.

"I want to see a young nation growing up that's healthy and fit.

"Sometimes if you don't deal with the problem quickly... then it just grows and grows and grows and gets worse," he said.

On obesity the prime minister added: "It's a huge problem and we've got to deal with it in a number of different ways.

"There are more school playing fields now. There is a wider range of sport in schools. Girls might be more interested in netball and yoga. It's one of the answers to childhood obesity.

"When I was at school, one child in the class was very fat and it was a problem for them. Now there are four or five in the class and it's a big problem for them."

Report

A report to be published this week will predict that half the population could be obese within 25 years and that the epidemic will cost the country £45bn a year by 2050.

On Sunday health secretary Alan Johnson said the problem is "a potential crisis on the scale of climate change".

Meanwhile, children's secretary Ed Balls told a Guardian newspaper-sponsored 'Healthy Kids Summit' on Monday that schools and parents must do more to halt the growing crisis.

"The way in which schools provide sports after 11 has a big impact on participation," he said.

"Particularly for girls... If you have a wider range of sports on offer, more alternative sports, more things like Frisbee or yoga which are as health driving as any other in schools.

"If the kit is awful or embarrassing it's much more likely the kids will forget to bring it."

Later this week Balls will publish plans to improve the take-up of healthy school meals, after new nutritional standards led to less children choosing to eat them.

But the minister said he would rather parents took responsibility for the situation than the government.

"I don't think it's sensible for parents to be shoving meat pies through the fence outside the school but I'm not going to come along and say they must have this standard [of food] in their packed lunch boxes," he argued.

"There are things I can do on nutritional standards, there are things schools can do to lead this forward, but at the end of the day, if parents aren't saying to children you need to have a healthy lunch, I can't demand parents take a different view.

"I have an instinctive reaction against anything that sounds like the nanny state and government ministers telling parents how to do their jobs. But at the same time... there are things we can do in schools to try to make sure children and young people and parents have got better choices and more information."