25 December 1916: birth of Edward Burnham, who played Professor Watkins in The Invasion (1968) and Professor Kettlewell in Robot (1974-75).
25 December 1984: birth of Georgia Moffett, daughter of Peter "Fifth Doctor" Davison (whose real name is Moffett); she has played Jenny, the Doctor's daughter, in The Doctor's Daughter (2008), Cassie Rice in animated story Dreamland (2009), Tanya in Big Finish audio Red Dawn (2000) and Alice in Big Finish audio City of Spires (2010).
25 December 1988: death of Terence Dudley who directed Meglos (1980) and wrote Four to Doomsday (1982), Black Orchid (1982) and The King's Demons (1983).
25 December 1999: death of Peter Jeffreys who played the unnamed Pilot in The Macra Terror (1967) and Count Grendel in The Androids of Tara (1978).
ii) broadcast anniversaries
25 December 1965: broadcast of "The Feast of Steven", seventh episode of the story we now call The Daleks' Master Plan. The Doctor and Sara get arrested at a northern English police station, but Steven busts them out; they then get embroiled on the Hollywood set of a silent movie; and the Doctor wishes "a happy Christmas to all of you at home!"
25 December 2005: broadcast of The Christmas Invasion, first full Tenth Doctor story. As the regenerated Doctor arrives in London, the Sycorax invade, but are repelled.
25 December 2005: launch of interactive game Attack of the Graske on the BBC website.
25 December 2006: broadcast of The Runaway Bride, first appearance of Catherine Tate as Donna Noble. Her wedding turns out to be a front for the release of the Racnoss; the Doctor flushes the spiders down the plughole.
25 December 2007: broadcast of Voyage of the Damned, first appearance of Bernard Cribbins as Wilfred Mott, with Kylie Minogue guest starring as Astrid Peth. Max Capricorn has persuaded the captain of the Starship Titanic to crash into Buckingham Palace, but the Doctor prevents them, at the cost of Astrid's life.
25 December 2008: broadcast of The Next Doctor. Back in 1851, the Doctor thwarts an invasion of England by Cybermen, with the help of Jackson Lake and Rosita Farisi.
25 December 2009: broadcast of The End of Time. The Master is resurrected; the Doctor returns to Earth via the Ood-Sphere and is captured by the Master in time to witness the transformation of the whole of humaity into duplicates of his arch-enemy.
25 December 2010: broadcast of The Christmas Carol.This makes 25 December, along with 1 January, one of only two dates in the year with seven broadcast Whoniversaries (and the only one where all of those Whoniversaries are actually Who rather than the spinoffs).
iii) dates specified in canon
As well as those mentioned yesterday:
25 December 1883: setting of Attack of the Graske.
25 December 1951: The First Doctor, Ian, Susan and Barbara steal the Stone of Scone (in "Set in Stone" by Charles Auchterlonie and John Isles, from the 2005 anthology Short Trips: The History of Christmas).