Following the downturn in international air travel due to the Gulf War, BA decided to take a step to "kickstart" the industry with "The World's Biggest Offer". It offered every seat for free to any international destination BA flew to on 23 April (St. George's Day). The whole campaign lasted some six months, and included seat sales, staff in clown's suits (since BA was crazy to be giving away seats for free), and the various aeroplanes painted with the titling. I remember watching television, and seeing an old lady who claimed it was her first time back in France since WWII; truly touching, and all because of "The World's Biggest Offer".
It was BA's biggest marketing campaign until "Making your money go further", launched just recently.