The Barber of Seville was a book Lafcardio found in a vacated cell in the Prison. Lafcardio considered using it to rebuild the library that had been destroyed in a fire. (PROSE: The Blood Cell)
The Barber of Seville was also an opera by Gioachino Rossini. The Sixth Doctor hummed a part of the aria "Largo al factotum" while on the Space Station Camera. (TV: The Two Doctors)