The former Beatle said cutting out meat consumption on one day a week could have a major impact on reducing global warming.

He argued that halving UK household meat consumption would do more to reduce emissions than halving the use of private transport.

Sir Paul, an outspoken vegetarian and animal rights activist who started his campaign in June, appealed for ‘people power’ to make the difference in the fight against global warming.

Kim Haywood, director of the National Beef Association, said Sir Paul's argument was "completely irresponsible". Beef and other meat was an important food which was an essential part of the diet for millions, she said.