25 July 1907: birth of Cyril Luckham, who played the White Guardian in The Ribos Operation (Fourth Doctor, 1978) and Enlightenment (Fifth Doctor, 1983).
25 July 1921: birth of Kevin Stoney, who played Mavic Chen in the story we now call The Daleks' Master Plan (First Doctor, 1965-66), Tobias Vaughn in The Invasion (Second Doctor, 1968), and Tyrum in Revenge of the Cybermen (Fourth Doctor, 1975).
ii) broadcast anniversaries
25 July 1964: broadcast of 'Kidnap', the fifth episode of the story we now call The Sensorites. The Doctor, Ian and Susan start to get to the bottom of the mysterious poisonings, but the internal political machinations of the Sensorites are reaching a conclusion as well...
25 July 1985: broadcast of first and second episodes of Slipback on radio. The Doctor has a hangover and Eric Saward thinks he is Douglas Adams. Episode two ends with Peri falling down a ventilation shaft, poor girl.
iii) dates specified in-universe
25 July 1794: setting of the end of "Guests of Madame Guillotine", all of "A Change of Identity" and the first part of "The Tyrant of France", the second, third and fourth episodes of the story we now know as The Reign of Terror.
A dance night was planned in Camden on Friday 25 July 2009, as seen in The Stolen Earth (Tenth Doctor, 2009).