The official said the government may in future recommend eating less meat as one of the "key environmental behaviour changes" needed to combat climate change.

The Department for Environment, Food and Rural Affairs (Defra) has already announced it is looking into the benefits of low environmental impact diets, including reducing the amount of animal protein eaten.

The email was written by an agency official to a member of the public who had written to support a vegan diet.

"Whilst potential benefit of a vegan diet in terms of climate impact could be very significant, encouraging the public to take a lifestyle decision as substantial as becoming vegan would be a request few are likely to take up," it said.

"You will be interested to hear that Defra is working on a set of key environmental behaviour changes to mitigate climate change. Consumption of animal protein has been highlighted within that work.

"As a result, the issue may start to figure in climate change communications in the future. It will be a case of introducing this gently as there is a risk of alienating the public majority."

Cattle and sheep release millions of tonnes of methane gas a year into the environment through flatulence. In New Zealand, for example the 55 million farm animals produce some 90 percent of the country's methane emissions.

Several European nations, including Germany and the Netherlands, have promoted policies that make methane capture a money-spinner for farmers.

In the UK, the National Farmers' Union, said it was working on similar projects, and rejected government moves to encourage less meat intake.

In a statement it said: "To suggest that people eating less meat and diary products will have a significant impact on the fight against global warming seems rather dubious."

Defra denied that it was telling people to give up meat. "It isn't the role of government to enforce a dietary or lifestyle change on any individual," it said.