Buffy the Vampire Slayer

 was a television series. By 2600, it was in its 792nd season. (PROSE: The Glass Prison)

Slake referred to Samantha Jones as "Buffy the Vampire Slayer" after she killed Weird Harold in San Francisco in 1997. (PROSE: Vampire Science)

Rose Tyler, while fighting a Mantodean, thought to herself, "Forget Buffy, this was Rose the Giant-Insect Slayer." (PROSE: Winner Takes All)

In the Main Hall of Geath, Rory Williams said that he and the Eleventh Doctor fought "the odd vampire", to which the Doctor replied, "Technically, they weren't vampires. Do I look like Buffy?" (PROSE: The King's Dragon)

The older Norman Bean from 2008 was said to be wearing "a T-shirt that said Duffy the Vampire or something," most likely a reference to the series. (PROSE: Homework)

In 2016, April MacLean references Hellmouths. (TV: For Tonight We Might Die)

In an alternate timeline, Lizzie Corrigan told Maxwell Edison that her Psychic Investigation Group (PIG) colleagues were fans of the series. (AUDIO: The Eternal Summer)

Behind the scenes
In promotional material prior to the release of the series, Class was advertised as a "British Buffy", particularly by Steven Moffat.