If we are to reach zero net emissions by 2050 the way we grow our food needs to be more efficient – farming and the way our land is used must change.

In the UK, about 20 per cent of farms produce 80 per cent of food and they do this on about half of the UK’s farmed land. The positive message from this is that we have some very productive farms in Britain, but there are relatively few of them.

About 80 per cent of farms don’t produce very much but use up 35 per cent of the British landscape. This is because taxpayer subsidies encourage people to farm poor land which will never produce much food, and because Britain gets less sunlight than most of our competitors making it harder for food to be produced competitively in a global market.

It is these farms that could most contribute by converting their farmland into nature – potentially reducing greenhouse gases by 30 per cent of what is needed to meet zero emissions.

The least profitable of these are sheep and cattle farms. These animals also produce methane, a greenhouse gas which is 24 times more potent than CO2, adding greatly to the growing problem of greenhouse gases from agriculture. They cause nitrate emissions which contribute to problems of air quality and pollute freshwater.

Apart from the pleasure given to us when we eat meat, it is hard to see where the benefits lie. A healthy diet needs only a small proportion of all the meat we produce. We have an option to change this radically as we leave the EU because we will have more control of how we produce our food. What could this look like?

Instead, we know enough about what good looks like to be able to incentivise today’s farmers to manage land very differently in future.

We should re-purpose poor agricultural land to different functions. These include carbon storage mostly in the form of peat and trees, water storage in upland landscapes to reduce flood risk further downstream, providing space for recreation which we know improves people’s health, and supporting wildlife which we value both for its own sake and because it shows us that we have healthy ecosystems.

Many of these so-called public goods could be achieved by changing the ways in which taxpayer subsidies are distributed. This is about paying to create landscapes which are both beautiful and which work for us all, rather than focussing on meat production as most of them do today.

Taxpayer subsidies can probably also be reduced over time because the market will eventually recognise the values being created. For example, many countries have pledged to reach net zero emissions by 2050 but the world is desperately short of carbon offsets.

Time is short if we are to ensure that land management is aligned with environmental goals. New legislation proposed over the next year is an opportunity to tackle both agricultural and environmental challenges at the same time and could be a foundation for rapid change over the next decade.

But there is another link in this argument which any policy needs to include. Losing 50 per cent of land to other functions will result in a 20 per cent loss of the food production capacity of the UK. We need to innovate to make up for this loss because it is unacceptable to export our environmental problems. New technologies for producing food, such as vertical farming, fermentation and the production of alternative proteins are on the cusp of being scaled up. Many are already common in supermarkets.

We need to invest in these innovations to make the revolution real.

The UK is at a fork in the road. It could continue with the current, failing, system of land use subsidy, perhaps staying aligned with the EU Common Agriculture Policy, or it can promote radical changes to prioritise the social and environmental goods from land.

Ian Boyd is a professor of biology at the University of St Andrews and former chief scientific adviser to the UK government