When I am tempted to write a parody, I have to have heard the original so many times that it seems "done to death" as it were. I also have to enjoy hearing the original well sung. I have been asked to sing MY version immediately after someone has just done the original, and I agree that it seems to be very bad manners to do so. I only sing parodies when the audience is well known to me, and very rarely when we are supposed to be entertaining "the masses" as it is definately an in joke that I am pulling.
Some of the Kipper versions take liberties with the metre and construction of the originals. This I do not like. It jars.
Most, however, are very well done.
Les Barker plays to folk clubs, and therefore his audience is likely to appreciate what he has done. In my everso humble opinion, Mr B is the most brilliant wordsmith alive today. So there!