Timeslides - S3-E5
Deliberate mistake: The Eagle on Hitler's briefcase is that of the (post war) Federal Republic of (West) Germany - not that of the Nazi German Third Reich. This was deliberate - showing the Third Reich Nazi emblem of an eagle holding a swastika would have had the episode banned in Germany, Austria, Poland and any number of other European countries. (00:08:25)
Other mistake: When Cat picks up the can of Leopard lager which is invisible to Lister, he shakes it, pops the cap and sprays Lister with foam. The foam is visible but the can remains invisible, and that makes no sense. If we are seeing the scene from Cat's point of view the can and foam should both be visible, and if it is from Lister's then neither should be.
Lister: Get real, man. Most eunuchs have got more balls than you.
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.