Sir John Houghton, the former chairman of the Meteorological Office and of the UN's scientific panel on climate change, said he had observed trials in New Zealand of genetically modified sheep designed to reduce the amount of methane they emit - from both ends.

The average dairy cow produces around 90 kg of methane per year

Sir John told the Oxford Farming Conference that methane from flatulent livestock still represented 20-30 per cent of the global warming problem.

He said that methane was produced in the stomachs of ruminants among other sources which were as yet imperfectly understood. He had observed experiments in New Zealand that had begun to address the problem.

"I saw a sheep with bags at both ends. I asked what was going on and they told me. This was proper science, you know."

Tests by New Zealand scientists had also shown that changing pastures could directly reduce emission of methane from sheep and cattle by as much as 16 per cent.

Source: Telegraph.co.uk