I am true Englishman, but not a true Scotsman.
And you’ve never say someone engaged in the act of masturbation was a “wanker”; You’d say they were “having a wank”.
Of course, “having a wank” can also, in some contexts, mean engaging in some self-satisfying and self-indulgent activity that has nothing to do with masturbation - for example, an artist making/displaying a particularly pretentious piece of work which is clearly intended to show just how very clever they think they are.
I think you may be sure that the number of MPs familiar with the works of Büchner and Alban Berg are not enough for such a usage to have any meaning at all (let alone effect) in parliamentary debate.
“Wazzock” is just one of many satisfying sounds vaguely indicating something less than intellectual and aesthetic excellence. Possibly there’s some distant mental association with “whiz” in the sense of yet another slang term for peeing, but I doubt very much if there’s any etymological logic behind it, or behind “plonker”, “twonk” and other such words.
Screwed up the joke, darn it. ::kicks dirt, muttering