The research came about when an Alwinton farmer refused to believe claims that New Zealand lamb was four times more environmentally friendly than its British counterpart.

So, just a few miles over the border in the Cheviots, organic farmer Graham Dixon and his conventionally farming neighbour John Snaith ran a survey on their upland sheep farms.

And the results show production on both farms is almost carbon neutral.

Mr Dixon said: “The findings are good news for upland sheep producers.

“Not only do we produce a high-quality, nutritious and healthy product, but retailers and consumers can be confident that the product has a low or negative carbon footprint at the farm gate.”

The New Zealand trials claimed their lamb was more eco-friendly in terms of greenhouse gases – including shipping the meat to Britain and delivering it to supermarket shelves.

Mr Dixon told TheSouthern: “That didn’t seem quite right and I thought ‘it’s our industry, we need to refute that’ – but there was no research.”

He contacted the National Sheep Association which agreed to fund the research, along with Northumberland National Park.

Oxford-based researchers used the free ‘carbon accounting for land managers’ calculator from rural business organisation Country Land and Business Association (CLA), and found that if the two upland sheep producers planted a few more hectares of trees, they would bring the carbon emissions from their farms down to zero.

Mr Dixon said: “I wasn’t surprised by the results because we know that we are a fairly low-input operation, as are most upland livestock producers, but the good thing is we actually have an answer to our competitors in New Zealand.”

The researchers found the main greenhouse gases from the farms were methane from sheep and nitrous oxide from improved grassland.

And they say existing woodland is able to offset almost all of the gases.

“The significance of existing woodland and of planting woodland on carbon sequestration was obvious,” the researchers said.

They found that if Mr Dixon, who runs 1,200 sheep on his 400-hectare Alwinton farm, planted 13 hectares of trees, he would bring the farm’s carbon emissions down to zero.

Neighbour Mr Snaith, who has Blackfaces on 500 hectares, would need a further 19 hectares of woodland.

The researchers concluded: “Improving the sustainability of sheep farms in the UK should focus on the feasibility of tree planting, and combine cropping/livestock production and the source and environmental impact of animal feed production ...