Image caption Obesity is a problem in low, middle and high income countries

Tougher action - including taxing junk food - is needed by all governments if the obesity crisis is going to be tackled, experts say.

The international group of researchers, who have published a series of articles in The Lancet, said no country had yet got to grips with the problem.

They said changes in society meant it was getting harder for people to live healthy lives.

And they warned without state action, health systems could become swamped.

Obesity-related problems, such as diabetes, were now accounting for between 2% and 6% of health care costs in most countries.

Rising spending

But as one of the articles showed, this is likely to get worse if current trends continue.

Researchers made projections for the US and the UK - two of the developed countries with the worst rates of obesity.

They predicted obesity rates would rise from a quarter in the UK to about 40% by 2030.

Such a scenario would cost the NHS an extra £2bn a year - the equivalent of 2% of health spending.

The rise in costs would be even greater in the US, where obesity rates would rise from one in three to about one in two.

The researchers accepted that the whole of society - from the individual to industry - had a role to play in tackling the problem.

But they said governments needed to take a lead by using legislation and direct intervention to create a better environment.

They said many measures - including taxes on unhealthy food, restrictions on junk food advertising, traffic light labelling and school-based education programmes - would save money as well as benefit health.

Others, such as providing obesity surgery and health programmes aimed at families with overweight children, would come with a minor cost although should still be looked at.

Oxford University expert Professor Klim McPherson, who was one of the lead researchers, said: "It is about changing the environment in which people live so they can make healthier choices."

Media playback is unsupported on your device Media caption Professor Klim McPherson from Oxford University: 'Obesity as serious as smoking'

But he said too many countries shied away from taking the right action and urged a forthcoming UN summit on health in September to "show leadership" by putting pressure on governments to act.

In particular, he criticised the government in England, which has been focusing on voluntary agreements with industry rather than legislation.

He said ministers were "enfeebled by their ideology" and too worried about accusations of the nanny state.

"They have this idea that government action in this sphere would not be a good idea," he added.

Professor Boyd Swinburn, who is based in Australia and works for the World Health Organization, agreed governments had been too slow to act on the "obesity crisis".

"There is more willingness to invest in drugs and surgery than dealing with the underlying causes."

He also compared the tactics of the food industry - in terms of getting people addicted to their products and in blocking attempts to discourage consumption - to those of tobacco firms in previous decades.

Of course we have to work with industry, but there is a feeling that the emphasis of this government has turned too far away from legislation Dr Frank Atherton, Association of Directors of Public Health

Dr Frank Atherton, president of the Association of Directors of Public Health, also said he was in favour of the interventions being suggested: "Of course we have to work with industry, but there is a feeling that the emphasis of this government has turned too far away from legislation."

However, Terry Jones, of the Food and Drink Federation, said the industry had been taking positive steps.

"The Lancet fails to recognise the lengths to which the UK food and drink industry has gone to help improve the health of the nation, particularly in relation to rising obesity levels," said Mr Jones.

Public health minister Anne Milton said the government believed the best way to achieve results was through a "collective voluntary effort".

She said this was achieving results, citing the pledge by industry to put calorie information on menus.

Media playback is unsupported on your device Media caption Public health minister Anne Milton: "We're too fat and we need to do something about it"

"We have no current plans to impose a 'fat tax', but we are working with food companies to reduce fat, sugar and salt and ensure healthier options are available.

"We also want to see businesses use more consistent and informative front-of-pack nutrition labelling than has been achieved in the past," she added.

"We recognise the significant threat that obesity poses to society and have taken a proactive part in improving health."