Back Home

In an unspecified parallel universe, "Back Home" was a song by the Beatles. Fitz Kreiner briefly considered singing in a bar in the prime universe, under the theory that the patrons wouldn't know it, and it would therefore seem to them like an original song. (PROSE: The Gallifrey Chronicles)

Behind the scenes
In the real world, "Back Home" was a multi-week #1 song in 1970, released in commemoration of England's performance in the World Cup, and sung by the 1970 side. The implication of this as a "Beatles song" is that, in Fitz' parallel world, the Beatles stayed together for longer than they did in the reader's world.