Revealing mistake: The metal shelf the three spare heads sit on can be seen to move as spare head three speaks. (00:19:40)

Revealing mistake: When it is revealed that the DNA modifier has made Lister smaller, Rimmer, Cat and Kryten all have shadows cast on the floor, but Lister does not. (00:25:25)
Answer: It's Queen Victoria, someone any Englishman would recognize, and needed no introduction.
Kryten was introducing the "people" to Rimmer. Rimmer isn't an Englishman; he's not even from Earth; he's from Io.