Toxic
From Tardis Wiki, the free Doctor Who reference
"Toxic" was a popular recording made by singer Britney Spears in the early 21st century on Earth. By the year 5 billion, the song was considered a ballad from Earth's classical era and was played on a vintage jukebox owned by Cassandra shortly before the planet Earth was destroyed. "Toxic" could be called the last song heard during the planet's history. (TV: The End of the World)
Behind the scenes
In the Children in Need sketch Looking for Pudsey, "Toxic" plays over the scene in which Britney Spears appears.