“Our current food system, and its future trajectory, is simply not sustainable, and we need to fundamentally change the way we produce food if we are to feed 9-10bn people in 2050 without wrecking the planet irreversibly.”

Those words were written by Pete Smith, Professor of Soils and Global Change at the University of Aberdeen, but they could have been written by any of the hundreds of people who have been researching the sustainability of our food habits during the last 20 years. Among environmentalists, food scientists, economists and others, a consensus has emerged: we have to change our diet—and change it in one respect in particular. There is simply not enough land or water on Earth to satisfy present, still less future, demands for meat, eggs and dairy products.

If we continue to try to meet that demand for food from animals, the damage will be catastrophic. The root of the problem is the sheer inefficiency of pastoral farming. It takes between five and 10kgs of grain to produce one kilogram of beef. That inefficiency shows itself in the massive amounts of land given over to crops like soya, which is fed to cattle.

It is estimated that animal farming is responsible for 80 per cent of global deforestation, and, a recent World Wildlife Report says, “60 per cent of global biodiversity loss is down to meat-based diets.” With regard to water, the Institution of Mechanical Engineers has calculated that it takes over 15,000 litres of water to produce 1kg of beef, while the relevant figure for 1kg of potatoes is 287. As water becomes an increasingly rare and precious resource, we cannot afford to waste it with such recklessness.

And then there is the question of greenhouse gases. Everyone knows that burning coal and oil raises the levels of carbon dioxide in our atmosphere, which is contributing to potentially ruinous climate change. But around 15 per cent of greenhouse gas emissions comes from animal farming. The only chance we have of meeting our targets for the reduction in greenhouse gas emission is through a radical change in our diet away from meat and dairy products and towards plant-based nutrition.

There is another compelling reason to make this change: health. Our animal protein-based diet is making us fat and clogging up our arteries with cholesterol, contributing to the steep rises in obesity and diabetes that we have seen in recent years in the UK, as well as resulting in the premature deaths of tens of thousands of people in this country due to heart disease.

Processed meat (certainly) and red meat (most probably) are also, according to the World Health Organisation, giving us cancer. Every 50g portion of processed meat eaten daily increases the risk of colorectal cancer by about 18 per cent, while every 100g of red meat eaten daily increases the risk by 17 per cent. A full English breakfast with two slices of bacon and two sausages will contain about 200g of processed meat—if you were eating that daily, you’d be close to doubling this risk.

The case for consuming less meat and dairy, then, is open and shut. Moreover, the situation is urgent. The director general of the UN Food and Agriculture Organisation, José Graziano da Silva, recently urged governments to adopt policies to reduce demand for meat and dairy consumption. But what is our government doing? Shockingly little. It doesn’t go much beyond reheating those familiar dietary guidelines about eating five portions of fruit and veg a day, something which only about a quarter of British adults actually succeed in doing.

The solution, I think, lies in the analogy between the present situation with regard to our diet and the situation 50 years ago with regard to smoking. I’m 61, and in my lifetime we have seen a massive change in smoking habits. Far fewer people smoke (16 per cent compared to 45 per cent in the mid-1960s), and therefore far fewer people are dying of lung cancer and emphysema. All sorts of government interventions have driven this—public information, punitive taxation, and a host of regulations, from banning cigarette advertising, to putting health warnings on packets and banning smoking in confined areas.

A similar range of measures could be used to persuade people to reduce the amount of meat and dairy products they consume. But there are positive measures the government could take. The government could make buying a burger both less attractive and more expensive. It could also make buying fruit and vegetables more attractive, by subsidising a marketing campaign, and also cheaper, by subsidising horticulture.

Economists from the universities of Bath and Surrey recently developed a mathematical model of the effects of such subsidies, which appeared to show that, by reducing the costs of healthy foods by 10 per cent, the government could save £6bn from the NHS budget at a cost of just under £1bn.

Over the years, the government has given us lots of encouragement to quit smoking. Now it needs to give us incentives with a less difficult switch—to start the day with oatmeal and berries, rather than sausage and bacon, and to feed ourselves beans, rice and vegetables, rather than that temptingly cheap and easy burger on offer at McDonald’s. Our health, and, quite possibly, the survival of the planet depend upon it.