We often hear that Britain produces around 60% of its own food. It is tempting to take that figure literally and say that if the population fell by 40%, the food we already produce would be enough for everybody who remained.

Mathematically that makes sense. In reality, though, the figure is far more complicated.

The latest Defra estimate says UK food production was equivalent to around 60% of the country’s food supply in 2025. With a population of roughly 69 million, that appears to represent enough food for about 41 million people.

But—and this is the important part—the 60% figure is based largely on financial value, not calories.

That makes a huge difference.

A kilogram of beef, cheese or soft fruit may have a relatively high financial value, but it does not necessarily provide as many usable calories as the same value of wheat, potatoes, oats or vegetable oil. We could theoretically produce 60% of our food by value while producing a considerably different percentage of the calories needed to keep the population alive.

In a genuine food emergency, value would become almost irrelevant. What would matter would be calories, protein, fats, vitamins and minerals.

We would need to ask:

  • How many calories are actually produced in Britain?
  • How much grain is eaten by people and how much is fed to animals?
  • How much food is exported or wasted?
  • Can the population receive a nutritionally adequate diet throughout the year?
  • Can production continue without imported fuel, fertiliser, animal feed, machinery parts and chemicals?

There is also a difference between food being grown in Britain and food being truly self-sustaining.

A British chicken may be raised here but fed partly on imported soya. British wheat may depend on imported fertiliser, diesel, pesticides and machinery parts. Even after food leaves the farm, it still needs processing, packaging, refrigeration and transport.

If those supporting imports disappeared, some home-grown production would continue normally, some would decline and some might stop altogether.

This gives us several different levels of food security.

Under normal conditions, British production has a value equivalent to feeding roughly 41 million people. If only half of that production could continue during a prolonged disruption, the equivalent falls to about 20 million. If only a quarter continued, it would be around 10 million.

For example, if Britain produced 50% of its food and only 10% of that home-grown production was genuinely sustainable without outside inputs, it would represent just 5% of the present national requirement—enough for roughly 3.5 million people.

That does not mean Britain could only ever feed 3.5 million people without imports. Agriculture could be reorganised.

Less grain could be fed to livestock and more land could produce potatoes, wheat, oats, beans, peas and vegetables for direct human consumption. Meat would become less common, although grazing animals could still make use of permanent pasture and upland areas unsuitable for crops.

With planning, rationing, lower waste and a more plant-based diet, Britain could probably support far more people than it could by simply carrying on with the present food system.

The real question is therefore not, “What percentage of our food is British?”

It is:

How many nutritionally useful calories can Britain produce, distribute and continue producing without relying on vulnerable overseas supplies?

Until food security is measured properly in calories and essential nutrients—not simply financial value—the familiar self-sufficiency percentage tells us much less than it appears to.