Organisations representing nearly every doctor in the UK have united in a single campaign to tackle rising levels of obesity.

The campaign will start by reviewing the case for fat taxes, promoting exercise, restricting food advertising and other measures.

They criticised sponsorship of the Olympics by fast food firms as sending “the wrong message”.

The Department of Health said it was taking action to combat obesity.

A spokesman for the campaign, Prof Terence Stephenson, said the government’s current strategy of “partnering” food firms in order to tackle obesity “might be seen as counter-intuitive”.

Almost a quarter of adults in the UK are thought to be obese and some predictions suggest half of children will be obese or overweight by 2020, with Prof Stephenson saying they were “storing up problems for the future”.

“This is a huge problem for the UK. It’s much bigger than HIV was, much bigger than swine flu.”

The Royal Medical Colleges and Faculties represent some 200,000 doctors across all specialities, from GPs to paediatricians and surgeons to psychiatrists.

They have described their campaign as an “unprecedented” union – as part of the Academy of Medical Royal Colleges (AoMRC) – on an issue of public health.

AoMRC spokesman Prof Stephenson said: “Every doctor I’ve ever spoken to feels obesity is a huge problem for the UK population.”

He said a united voice had “more of a chance” of tacking obesity.

The first phase of the campaign will try to find out what works. It will review evidence for diets, exercise, taxation, minimum pricing, changing advertising and food labelling, which medical procedures work and how children are educated.

Recommendations could target food companies who sponsor major sporting events – such as the Olympics – and fast food outlets which operate close to schools.

Prof Stephenson said allowing companies such as Coca-Cola and McDonalds to sponsor the London 2012 Olympics “sends the wrong message.”

“They clearly wouldn’t be spending the money if they didn’t benefit from being associated with successful athletes,” he said.

A McDonald’s spokesperson said the Olympics was “the biggest catering operation in the world,” adding: “Sponsorship is essential to the successful staging of the Olympics.”

Prof Stephenson told the BBC a campaign to persuade people to eat healthy food might work in the same way as the current anti-smoking drive.

There have been heavy restrictions on advertising smoking in the UK, on TV and at sports events, and a consultation is being launched on whether cigarettes should be sold in plain packaging.

“It’s much more likely, as in smoking, that the solution will lie in changing the environments, changing the way people are exposed to marketing, advertising and pressures to buy these kinds of foods,” he said.

“Another aspect of that is the taxation of cigarettes to deter people from buying them – that seems something we should look at in relation to food,” he said.

However, Prof Stephenson said he did not think society could simply exercise its way out of the problem of obesity.

“My own personal experience is you have to exercise a huge amount to lose weight, I would have to run on a treadmill at maximum speed for an hour to counter-effect the calories from one or two Mars bars.

“Most people in modern life just don’t have the time in our lives to spend several hours a day exercising.”

These are not the final recommendations of the doctors groups. The plan is to spend the next three months gathering the evidence.

The Department of Health said it welcomed the colleges’ “emphasis on obesity as this is one of our key public health priorities,” and highlighted the change4life campaign to encourage healthier living, and the “responsibility pledge” by some food and drink companies to improve public health.

A spokesman added: “We are committed to identifying the best possible evidence of what works in tackling obesity which everyone across the country has a role to play in and we look forward to seeing the evidence of the Royal Colleges inquiry.”

Prof Stephenson said there was nothing wrong with the government working with food manufacturers to improve public health “but to rely on the industry seems counterintuitive”.

Prof Sir Neil Douglas, chair of the Academy of Royal Medical Colleges, said: “This won’t be just another report that sits on the shelf and gathers dust. It will form the bedrock of our ongoing campaigning activity.

“We are absolutely determined to push for whatever changes need to happen to make real progress in tackling obesity – which is why we’re casting the net wide to get input from a range of organisations and individuals.”