They may have done, just like the Tories may have done ( remember Nicholas Ridley ? ) But Labour and the Tories, in addition to the LibDems, are not a one-trick pony, like The Man in the Pub, and UKIP.
Every time one of his more nutty slices of fruitcake escapes from the cake tin, Farage appears on Newsnight, or CH4 news, and feins horror and pledges that it won't happen again.
Until it does happen again, sometimes just days or hours afterwards. These kind of people are attracted to UKIP because they feel at home there, and, more importantly, they think that they can work undetected and unmolested.
Well, undetected until they open their mouths and put both feet in, like this latest idiot has done. Did he really think that he could insult Lenny Henry, a well-loved British entertainer and get away with it ? The answer is, yes, he thought he could, and that speak volumes about UKIP and what it stands for.
Not long ago, Farage said that all UKIP candidates had to sign a declaration that said that they were not a loony. But recent events have shown that this was just a PR exercise, to throw the media of Farage's back for a few days.
I have made this point before but managing UKIP is akin to herding cats, an next to impossible task.