Here’s a brief extract from a David Jacobs interview with Ysanne Churchman, who provided the voice of Alpha Centauri in the two Peladon stories:
You use your voice in a variety of ways. You’ve been called upon to make some very strange voices, but I would presume that Alpha Centauri in ‘Doctor Who’ was the strangest?
That was the hermaphrodite hexapod Alpha Centauri. Stuart Fell, the stunt man, was in the clothes of course. We used to have little discussions as to how he was thinking and feeling.
What was your brief? How did you come across that voice?
Well, I was told they wanted the voice of a young boy, with the mentality of a homosexual civil servant! (laughs) So that was how it was for the first serial, then for the second one they said they wanted it exactly the same, but he’s 130 years older!