See http://news.bbc.co.uk/onthisday/hi/dates/stories/april/1/newsid_2819000/2819261.stm .
Way back in 1957 the BBC ran a spoof Panorama programme about the spaghetti harvest. The programme was narrated by Richard Dimbleby. It was the first time, I think, that TV had been used to pull an April 1st stunt.