If you imagine a healthy future for Britain, or any other country that has put the hunger of millennia behind it, you see a kind of dictatorship. Not a tyranny, but a society that ruthlessly restricts free choice. It is a future that views the mass of people as base creatures jerked around by desires they cannot control. Expert authority must engineer their lives from above for their own good and the common good.

That we need to change radically was shown by a mass study of the health of 300,000 people that was at once entirely shocking and wholly predictable. Newcastle University found obesity and the lack of exercise (the two go together, of course) in the middle aged mean two-thirds will have more than one chronic illness when they reach 65. These bleakly titled “multiple morbidities” will afflict them simultaneously. (For in the future, illnesses will not come as single spies but in battalions.) Most are the natural consequence of our high calorie/low exercise world: arthritis, cancer, diabetes, dementia and strokes.

Here’s my partial sketch of how Britain would have to change to limit the costs to the NHS that stunted lives and avoidable pain will bring. Pedestrians and cyclists would have priority on the roads. If the roads are too narrow to take cars, cycle lanes and a pavement wide enough to allow pedestrians to walk or run in comfort, then cars will have to go. School runs will become history as heads refuse to admit any able-bodied child who arrives at school in a car.

It will not necessarily be illegal to drive in towns and cities, just pointless. Motorists would inch along because cycle and bus lanes would take up road space and pelican crossings would be reset so pedestrians never had to wait more than a minute to cross a road. Even when they reached their destinations, drivers would search forever for a space because car parks would have been demolished and replaced with public parks.

No fast-food outlet would be allowed within a one-mile radius of a school. Agricultural subsidies for fat and sugar would be abolished. Rapeseed oil and sugar beet cultivation would stop as new subsidies for public transport began. Meanwhile, the manufacturers of processed food high in sugar, salt and fat would face advertising bans and punitive taxes. (If food manufacturers want to dump prematurely sick patients on the NHS, we will say, they can damn well pay for the privilege.)

Water fountains would everywhere provide an alternative to drowning in the calories of fizzy drinks. Wardens would patrol parks, so the elderly would not fear walking in them and the young fear playing in them.

It may seem a less practical measure but I would hope to see a vigorous challenge to the paradox of our culture’s celebration of thinness and athleticism in an overweight world. The idealisation of film stars and athletes raises impossible expectations. Because 99% of people do not have the genes – or the time and money for training – to even think of imitating them, we simply don’t try. A small blow could be struck if UK Sport were forced to stop sponsoring elite Olympic athletes and spend its millions on sports facilities for all instead.

The above may sound utopian or dystopian, according to your point of view, but more radical ideas are circulating. In 2006, Tim Lang and Geof Rayner from the Food Policy Centre said the vast forces in the modern economy delivering calories on a scale humans did not evolve to digest required an equally sweeping response. Everything from our attitude to nature, our bodies and food production needed to change. The Brazilian nutritionist Carlos Monteiro coined the concept of “ultra-processed” food: ready-to-eat or ready-to-heat dishes, snacks and drinks that are energy-dense, depleted of nutrients, fatty, sugary or salty.

Included among them I must warn you were not only Big Macs, but the middle-class wares of Marks & Spencer and Waitrose. As for the notion of living in an “obesogenic environment”, which combines the cheap calories of fast food with the inertia office work and the car brings, it was first described and denounced in the mid-1990s.

Facebook Twitter Pinterest One day all this could be a thing of the past. Photograph: Martin Godwin/The Guardian

Ever since, nutritionists have hoped for a moment of public enlightenment. They consoled themselves with the thought that it took decades for the link between smoking and lung cancer to turn from a medical fact into an effective public health campaign. But the years have passed and in Britain little has been done. Councils have built the odd cycle lane and a modest sugar tax is due in April. The real work, however, has yet to begin.

I can feel the force of the objections. When we imagine a healthier future we are also imagining a more authoritarian state. Individual choice will be constrained and wisdom of the crowd rejected. Women will wonder who will chop the vegetables and cook the dinners when ultra-processed food is taxed to the point of extinction.

Beyond gender lies an undoubted class element in public health campaigns. Sugar and fat addiction, like all addictions, provide a temporary respite for the poor, the depressed and the disappointed. Perhaps we should offer them better lives rather than snatch away the few comforts they enjoy. This sounds a stirring counter-argument. But as any reader who has been an addict will know, addiction prevents you finding a better life. For when you suffer the multiple morbidities of diabetes, arthritis, cancer and strokes, your sicknesses are your life. You do not have the freedom to choose to change it.

God knows, there are good reasons to mistrust experts re-engineering societies from above. But as with tobacco, freedom of choice in the food and car markets has left us with no choice but to trust them.