i) births and deaths

24 December 1925: birth of Innes Lloyd, producer of Doctor Who from The Celestial Toymaker (First Doctor, 1966) to The Enemy of the World (Second Doctor, 1967-68), who overhauled the show by getting rid of all the regular cast including the star, thus ensuring its long-term survival.

24 December 1941: birth of John Levene, who played Benton in various UNIT stories from 1968 to 1975.

ii) broadcast anniversaries

24 December 1966: broadcast of second episode of The Highlanders. Polly and Kirsty capture Ffinch; the Doctor tricks solicitor Grey; but Ben, Jamie and the Laird are trapped on the slave ship.

24 December 2006: broadcast of Combat (Torchwood), the one with the fighting Weevils which was written by Noel "Mickey Smith" Clarke.

iii) dates specified in canon

Most of the Christmas specials actually begin on the 24th:

24-25 December 1851: setting of The Next Doctor (Tenth Doctor, 2008).

24 December 1869: setting of The Unquiet Dead (Ninth Doctor, 2005).

24 December 1892: The Eleventh Doctor and Clara encounter the Great Intelligence in The Snowmen (Eleventh Doctor, 2012).

24 December 1938 and 1941: setting of The Doctor, the Widow and the Wardrobe (Eleventh Doctor, 2011).

24-25 December 1968: setting of much of the action of Mark Gatiss' 1992 novel Nightshade.

24-25 December 2006 (?): setting of The Christmas Invasion (Tenth Doctor, 2005).

24 December 2007 (?): setting of The Runaway Bride (Tenth Doctor, 2006) and the start of Turn Left (Tenth Doctor, 2008).

24-25 December 2008 (?): setting of Voyage of the Damned (Tenth Doctor, 2007).

24-26 December 2009 (?): setting of The End of Time (Tenth Doctor, 2009-10).