Great Fire of London

The Great Fire of London was a massive fire started when a Terileptil weapon overloaded in a bakery on Pudding Lane, London on 2 September 1666. (PROSE: Doctor Who and the Visitation) The Fifth Doctor and his companions Adric, Nyssa and Tegan Jovanka left the scene while Richard Mace attempted to put the fire out. The fire proved helpful in clearing plague from the city. (TV: The Visitation) A later incarnation took credit for the fire, but stated it was completely necessary. (COMIC: Black Death White Life)

Prior to witnessing the cause, the Doctor had been accused of starting the fire. (TV: Pyramids of Mars) The Fourth Doctor witnessed the outset of the fire at a distance and urged the Republicans and the forces of Charles II to stop fighting and work together to put out the fire. Sergeant Mullens, suspicious of the strangeness of the Doctor and Sarah Jane Smith attempted to arrest them for starting the fire. (PROSE: The Republican's Story)

Shortly thereafter, George, Helen, Ida and Alan Mortimer were rescued from the Great Fire by the First Doctor. It is possible that, for a brief period after the First Doctor's arrival, there were three separate incarnations of the Doctor co-existing in the same time period and in close promixity to one another. (PROSE: Doctor Who and the Invasion from Space)

In the aftermath of the Great Fire, the English Catholics were falsely accused of having started it. (AUDIO: The Glorious Revolution)

The renegade Time Lady Iris Wildthyme claimed to have been present for the Great Fire. (AUDIO: Excelis Dawns)

A column at the bottom of King William Street — close to the Bank of England building in the City — commemorated the event. Its plaque, however, neglected to mention the Doctor's involvement in the tragedy. It read in part:
 * "In the year of Christ 1666, on 2 September, at a distance eastward of this place of 202 ft, which is the height of this column, a fire broke out in the dead of night which, the wind blowing, devoured even distant buildings, and rushed devastating through every quarter with astonishing swiftness and noise…" (PROSE: Matrix)

As the Terileptil involvement was equally unknown, it was widely believed that the people of London were so scared they set fire to London. Alistair Gryffen noted this as an example of events concerning the spread of fear. (TV: Fear Itself)

Behind the scenes
The date of 2 September is derived from prose sources. It's Matrix and the novelisation of The Visitation, not the serial, that give the specific date. The novelisation's rendition of the scene in episode one where the Doctor and Nyssa are sneaking around the manor house contains a line where he claims it's the first of September. Since night falls during the course of The Visitation, it's reasonable to assume that the Great Fire occurs on 2 September. Matrix takes away all guesswork by quoting a commemorative plaque which flatly gives the date.