It is this: "The third great and bountiful human empire".
We've returned to this several times already, and it's always presented as a good thing with - whoops - something rotten below the surface in just this episode. Or, as with the Ood, something wrotten in all three galaxies with people not questioning where the Ood came from.
But, generally, good.
But: "Great and bountiful human empire"? Well, "Empire" is worrying, but more worrying is the label "great and bountiful".
I'm sure there's a principle of politics, which I've seen written down but can't remember who claimed credit for it, that if you name yourself something, you're not that thing. Like "German Democratic Republic" (East Germany) or United Soviety Socialist Republics, or United States of America, which can now claim one civil war, innumerable doomsday cults, and more racial division than South Africa through sheer persistency of hate groups. Also United Kingdom, which includes Northern Ireland and Scotland, where they now have their own parliament and are edging towards full independence.
Why hasn't the Doctor stopped halfway through explaining things to any of his assistants so far and said "Hang on, that's worrying..."