The debate around the climate impact of farming has been reignited after the former chief scientist to Defra said half of the UK’s farmland should be rewilded to help tackle the climate crisis.

Sir Ian Boyd told the Guardian that restoring 50 per cent of farmland into woodlands and natural habitat could mean the amount of cattle and sheep would fall by 90 per cent. He estimated this would result in 20 per cent less food being produced, which could be replaced by developing vertical farms, he said.

The comments put him in direct opposition with the National Farmers Union, which has set out plans for agriculture in the UK to reach net zero carbon emissions by 2040 without reducing livestock numbers.

Instead, the NFU said precision techniques, greater efficiencies, production of plant fuel on farms, and feed additives for cattle, would help the sector reduce and offset its carbon.

Globally, agriculture is estimated to contribute around 13 per cent of carbon emissions and a series of peer-reviewed studies have recommended reducing intensively-produced meat and dairy intake as one of the best ways to reduce carbon footprints. The UK’s farming sector has fought to demonstrate that its largely grass-based livestock systems have a much lower footprint due to carbon storage potential and lower inputs.

Responding to Boyd’s comments on twitter, NFU president Minette Batters said: “It took two world wars to realise the error of not being able to produce enough food for our island nation. I said [at the Oxford Farming Conference] last year you only turn the food production tap off once. We cannot make the same mistake again."

Another farmer, Joe Stanley, tweeted that: “Rewilding 50% of GB farmland will just offshore our food production to countries with [lower]️ environmental standards.”

The debate is likely to escalate further with news of Channel 4’s upcoming documentary, Apocalypse Cow, due to air on 8 January and fronted by George Monbiot, a leading proponent of rewilding, which he said would set out how farming as we know it could end within decades.

In a recent interview with Wicked Leeks, Monbiot said food losses caused by less production in the UK due to rewilding could be mitigated by developments in lab-grown and cultured proteins, for foods like palm oil and fish. “It could be the crucial technological change that allows us to stop both climate and ecological breakdown,” he said.