Southwark has a good claim to the title of Britain's child obesity capital. The London borough has the highest number of overweight 11-year-olds, with children up to the age of 15 in the top 5% for body mass index.

Perhaps that is why one of its primary schools, Ivydale, is working hard to change pupils' eating habits. Evelina Dimopoulou, the assistant headteacher, has introduced a reward mechanism. Children with a fresh piece of fruit in their packed lunch – or those without a packet of crisps or a chocolate bar – are given a sticker.

At one point I was astounded to witness a six-year-old run up to the teacher and say: "Miss, Mummy put this packet of crisps in my lunch box. But I know it's bad for me, so I am not going to eat it. Can I have a sticker?" The child flung the packet into the bin.

Dimopoulou says the key is to inform, educate and empower the children to make the right choices. It sounds simple, but it is a message that needs to be loudly delivered; it shocks me to see children snacking on crisps and chocolates every day.

I was invited to speak to the children in my capacity as a cardiologist about healthy eating and the adverse effect of junk food on the heart. The innocent young minds appeared interested in my basic biology lesson explaining that the heart acting as a pump was responsible for allowing them to run around and that eating unhealthy foods would interfere with that process by making them gain excessive weight.

Jamie Oliver was especially interested to hear about my visit. He had invited me as one of a number of health experts to discuss what more needs to be done to tackle the worsening obesity epidemic. Our gathering included Professor David Haslam, chair of the child obesity forum, and Professor Terence Stephenson, chair of the Royal College of Paediatrics.

A very passionate four-hour discourse ensued, with some emphasis on the need to increase integration between health professionals and schools. And this would need to be backed up by enabling the teaching profession to reinforce the message.

There are some obvious discrepancies in the campaign to promote healthy eating. The government awards healthy school status to those that meet its guidelines – but it does not include control over what food children bring from home.

What's more, while all maintained schools are required by law to comply with food standards, non-maintained and independent schools are not obliged to do so. So for 580,000 children educated privately, it is up to their schools to determine standards. Also, academies set up from September 2010 do not need to comply with the standards and are free to promote healthy eating and good nutrition as they see fit.

The government needs to be more accountable. The School Food Trust, which advises it, has made inroads in improving nutritional standards of school dinners but most children in primary and secondary schools take in packed lunches where there is no regulation. This is why that Southwark teacher has taken matters into her own hands.

However, genuine health promotion needs to spread outside the school gates. Judy Hargadon, the chief executive of the trust, agrees. "I would love to see eating a balanced diet become the social norm for children. School is the best place to help families do this. Parents should support schools when they are trying to improve the food our children eat."

The shopping centre closest to Dimopoulou's school offers two choices for lunch: Pizza Hut or Burger King. And these are places packed with families each weekend. Supermarkets hardly help – placing snacks such as crisps and chocolates in prominent positions. Fast-food restaurants not only proliferate, but McDonald's is a main sponsor of the Olympic Games.

Food corporations often focus on personal responsibility as the cause of the nation's unhealthy diet and raise fears that government action challenges freedoms. But this obscures the reality that some of the most significant health advances have been made by population-based public health approaches in which the overall welfare of the population trumps certain individual or industry freedoms.

The public smoking ban is a prime example. It has already had an impact on reducing cardiovascular mortality. However, this legislation occurred decades after irrefutable evidence linking smoking to lung cancer and heart disease entered the public domain. Through powerful lobbying Big Tobacco was able to defend half a million deaths a year caused from cigarettes by provoking fears that freedom and choice were threatened – the sort of arguments now used by the food lobby.

In 2004, the World Health Organisation declared obesity a global epidemic. Eight years later the statistics tell us that not only are we failing to tackle the issue but it's getting worse. There are now 1 million morbidly obese people in Britain. Trends suggest that without effective intervention nine out of 10 adults, and six out of 10 children, will be overweight or obese by 2050. The association between diet and heart disease and cancer is irrefutable. Indeed, it could be argued that diet-related ill health is set to cripple the NHS.

Last year, the government argued that working with the food industry, including McDonald's and Pepsi, was the best way forward. I have never heard such rubbish. Allowing food corporations to self-regulate has not only been ineffective but in some instances dangerous. The recent highlighting of the "one of your five a day" logo on some tinned food items, high in sugar and fat, is a good example.

People can be easily misled by "healthy" marketing. Not only is it a reflection of corporate greed taking precedence over the health of our children but it may also be part of the explanation of why, despite the greater information on food packaging, our obesity rates are soaring. Current food labelling is confusing for many.

Appointing an obesity tsar who can act independently of political or commercial interest would be a step in the right direction. In fact, it's high time that the government implemented not one but a series of robust measures through legislation to tackle this worsening crisis.

Imposing legislation to tax unhealthy foods is long overdue. That was the call from Professor Robert Lustig, a child obesity expert, following news that consumption of sugar had trebled worldwide in 50 years. Not allowing children to bring junk food to school should be a policy introduced across the board, with no exceptions.

I also call on the Department of Health to ban vending machines selling chocolates, fizzy drinks and crisps from hospital grounds and leisure centres – places that are supposed to be environments to promote good health and wellbeing. Let's stop sending out the wrong message.

The government's health reforms have rightly come under fire for threatening the National Health Service. But they fail in another fundamental respect: they do little to tackle the major contributors to premature death: obesity, alcohol misuse and smoking. These can only be addressed effectively by tackling fast food advertising (and the marketing of alcohol as glamorous, and tobacco displays in large supermarkets).

Perversely, the Tory-led coalition is seeking the assistance of fast-food and drinks corporations to help draft strategy in public health reforms. The idea is to replace state intervention with private and corporate action.

It is therefore no surprise that public health leaders have emphatically called for the health and social care bill to be dropped, as they rightly believe this callous and inept strategy will take us backwards in tackling one of the greatest health challenges facing the west.

It's time to listen to the experts, Mr Cameron – the teachers, doctors, nurses and academics. If you don't, we will succumb to the perils of ignoring history, where Big Tobacco played dirty and millions died. For Big Tobacco, should we now read Big Food?

Dr Aseem Malhotra is a London cardiologist