This is a very strong, very important and long-awaited message. We know about the energy balance equation — balancing calories taken in with those burnt up with exercise — and the importance of both sides. But the question that has never adequately been answered is which one is more responsible for the obesity epidemic.

The situation in Britain is identical to the United States; it is just we are about a decade behind. There are the same forces and the same drivers in our hideously obesigenic environment: the availability of food at all times, day and night, wherever you are in your community, and the size and cheapness of portions, and their increasingly unhealthy content.

In the past, research such as Gluttony or Sloth, published in the British Medical Journal (1995), has tended to suggest that physical activity is the problem. Unfortunately that has provided the food industry with a mind-numbing mantra that it is nothing to do with them. Only in the past few years have they taken a more responsible stance and fessed up to their part of the problem.

The reason physical activity was blamed was because food taken outside the home was notoriously difficult to measure. But we all knew that there was more fast food, more meals out, more snacking. Intuition said more food was to blame, its astonishingly poor quality, and our grazing and bingeing habits. This research squares the circle. It takes into account all the things — ubiquity of food of unhealthy varieties and quantities.

We are seeing some culture change within certain parts of the food industry — in the quality of food, such as salt and fat levels, and some labelling. But research such as this is powerful as a driver for change — to say to the food industry that, yes, what you are doing is fine, but let’s do it more widely, more vigorously, more comprehensively. Don’t just pay lip service to it. This must be the beginning of a rolling programme of improvement.

Exercise is good for you and that drive should be continued and promoted as much as possible among children and adults. But do not expect it to solve the obesity problem. The Government must have enough political will not just to make a couple of small changes but to develop a consistent long-term strategy.

All Government policies have been about the prevention of obesity. It is too late to prevent obesity in this country — it is like standing in a blazing house fire and calling in Health and Safety to check your plugs and wiring, when what you need is the fire brigade. Because if obesity prevention is 100 per cent successful, and no one gains another pound, we will still have an epidemic of diabetes within the next ten years, followed by an epidemic of heart disease and premature death.

- Dr David Haslam is a GP in Hertfordshire and chair of the National Obesity Forum

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