Prince Philip was at a Worldwide Fund for Nature function in Canada in 1983 when a McDonald's official was introduced. Prince Philip allegedly replied: "So you are the people who are tearing down the Brazilian rain forests and breeding cattle."
The official denied the charge, to which Prince Philip is said to have replied "rubbish" before storming away.
Prince Philip's alleged outburst was brought to light by Dave Morris and Helen Steel who are accused by McDonald's of libel. The American burger company accuses the "McLibel Two" of distributing a leaflet which allegedly claims McDonald's is responsible for acts of environmental destruction and its food is partly responsible for cancer, heart disease and diabetes.
The two unemployed environmentalists from north London, who are defending themselves, deny the accusations but claim they are a fair comment on the company's activities.
Following Prince Philip's outburst, McDonald's issued an edict that no McDonald's plant was to use Brazilian beef. Later Prince Philip clarified his remark by saying it referred to a "story" he had heard at a "rainforest symposium".