April Fools' Day

April Fools' Day was a holiday celebrated on 1 April. On this day it was customary for people to play practical jokes and hoaxes on one another.

On 1 April 1963, Ian Chesterton sent one of his Coal Hill School students, Little Titch Critchley, to the supplies cupboard for "a left-handed blackboard rubber". Later that morning, Ian started a snowball fight with Mr Okehurst, shouting, "April fool!" That afternoon, when John Brent tried to tell his father about the snowmen which had been animated by the Cold, Captain Brent thought his son was playing an April Fools' joke. (PROSE: Time and Relative)

April Fools' jokes in the real world

 * An issue of the Doctor Who fanzine Dream Watch Bulletin said there was a sixth episode of The Dæmons planned which would feature escaping UNIT.
 * An issue of Doctor Who Magazine reported that an attempt was made to colourise parts of The Tenth Planet.
 * 2009 - As an April Fool's joke, word circulated around the Doctor Who set that Michael Jackson was paying a visit. (REF: Doctor Who: The Writer's Tale - The Final Chapter)