There was a short piece on why Earl Grey tea is so named on Radio 4's Pick of the Week earlier (listen here for another week - the piece begins at 05:58). Earl Grey is a rather elegant tea with a distinctive bergamot-orangey flavour.
Charles, Earl Grey was the British prime minister from 1830 to 1834. One of his envoys, while in China, supposedly saved a mandarin's life, and, in gratitude, the mandarin gave him a special tea recipe. The envoy duly passed the recipe on to the PM, who sent it to the tea-making firm Twinings to make up the recipe. The prime minister seemingly liked the tea and asked for another batch at a later date. Twinings had written the recipe down, so when Grey ordered it, they referred to this recipe as Earl Grey's tea.
The snippet on the radio was from a series, The Prime Ministers, presented by the BBC's political editor Nick Robinson (here's the Earl Grey episode). Twinings website carries the story, too. The story on the Tea Council's website is slightly different; they say it was Jackson's of Piccadilly who first created the tea.