Thanks. I should amend the entry to clarify that.
The point is the -er ending signifies the French path, while the -o ending the Spanish. In the Hellowes citation he translates the Spanish negros as Nigers.
As for Clarkson, his “apology” is more of the “non-apology apology” variety than an actual one. He did use the word. The offense is not in the combination of phonemes; there is nothing magical about any particular set of sounds. What’s offensive is the word’s long history as a term of abuse, and mumbling or coughing as one uses it is in some ways worse that speaking it clearly. In doing so the speaker is trying to have it both ways, relying on the offensiveness of the term to titillate the audience and boost ratings, while deliberately creating a translucent veil of deniability to protect oneself. I’m not saying he should be sacked over this, but he is not guiltless. He’s a professional broadcaster. He should know better.
Growing up in New Jersey in the 1960s, the form of the rhyme we used most often was “catch a tiger.” We certainly knew the offensive version, and I did hear it on many occasions (and probably used it myself), but even as kids we knew it was a really bad thing to say and avoided it in the normal course of our play.