“Land sparing” could lead to dramatic increases in wild bird populations, according to research that bolsters the case for rewilding.

Farming intensively to increase yields while turning over much larger areas of farmland to wildlife could – if combined with measures to cut food waste and meat consumption – would meet Britain’s food needs and more than double the populations of breeding birds.

It has been calculated that farmed land in Britain must increase by 28% if it is to supply the growing demand for food by 2050. Andrew Balmford, a professor of conservation science at the University of Cambridge, said this conundrum could not be solved by just reducing demand for food – yields must be raised too.

Increasing yields is controversial among some conservationists who argue that intensive farming is unsustainable. Upland farmers also object because they fear land sparing will force them to give up farming and rewild their hillsides, while the fertile lowlands are intensively farmed.

In research presented to a rewilding conference organised by the Cambridge Conservation Forum, Balmford and a team of researchers studied food production and birdlife on the Cambridgeshire Fens to model how a far greater area of farmland could be devoted to wildlife.

By halving food waste and meat consumption, the UK could farm less intensively – in a more wildlife-friendly way – on the current farmed area while retaining the 5% of land “spared” from farming and given over to nature reserves. If this was done, the populations of 101 British bird species would on average increase by just under half.

But if yields were increased on a quarter of farmland to the highest levels presently found on the Fens and, alongside demand-reduction measures,another 25% was farmed in a nature-friendly way, this could also meet future food demand. This would allow half the remaining land to be devoted to wild nature.

By dramatically increasing spared land from 5% to 50%, bird populations soared on average by approximately 250%, with species such as bitterns and bearded tits prospering on rewilded fenland. The quarter of land cultivated by traditional, low-intensity farming was important for conservation too: this helped bolster farmland species such as the grey partridge and yellowhammer.

“We’re not arguing for business-as-usual industrial farming but we have to be mindful of yield,” said Balmford.

He said there was a risk that post-Brexit payments for farmers could improve Britain’s landscape but reduce food production, leading to more food being imported from countries where the environment is being destroyed.

He said: “We need a twin-track where we get serious about using some of our landscape in a way that’s much better for biodiversity and ecosystem services but that must be linked to incentives enabling some farmers to be productive in sustainable ways on remaining farmland. If we don’t, it’s a sleight of hand – we’ll just buy our food from somewhere else and offshore the problem.”

While organic farmers and most conservationists fear raising yields would lead to more environmental damage such as greenhouse gas emissions and increased nitrate pollution, recent research by Balmford and colleagues found that in four types of farming, including European dairy farming and wheat production, intensive systems were often less polluting per unit of production than organic and low-intensity agriculture.

But Balmford said there was not enough data on other “externalities” such as soil erosion to measure the full, long-term costs of high-yield farming. On the Fens, for instance, there is scant data on soil erosion. The Fens’ fertile, peaty soil being washed away or eroded by the wind could prevent high-yield farming in the future.

If land sparing is taken up in the post-Brexit farm payments being developed by the environment secretary, Michael Gove, some fear it could lead to unprofitable upland farms being turned over to nature while fertile lowlands are intensively farmed.

This was criticised at the conference by Dafydd Morris-Jones, a Welsh hill farmer who said land sparing was quite attractive if you were a large-scale grain farmer, “because it’s your land that will be concentrated on to be productive and our land that won’t”.

Morris-Jones said he would prefer to see land sparing used within individual farms. “With better conversations, more nuanced thinking and a great deal more data, the uplands would be able to provide sustainable food while providing ecological and environmental benefits. I don’t think they are in conflict.”

Morris-Jones accused rewilding of being “eco-colonialism” forced upon Welsh upland farmers by the English, pricing out locals and eroding their landscape, culture and community.

“Rewilding has become a toxic term in mid-Wales,” he said. Of the argument that upland farming could be replaced by ecotourism, he said: “I can’t see how careers in the voluntary-supported Wildlife Trusts or low-paid and exceptionally seasonal work offered by the tourism industry will pay the mortgage. As for payments for ecosystem services and public goods, I just don’t think it will be capable of sustaining that richly varied rural economy that we rely upon to keep our culture, language and community alive.”