I've never heard that. A quick google dredged up the following, is this the one ? It would certainly be amusing to be taken unawares by it at Cropredy.
A lot of beer has flowed under the bridge since those days, so I'm not ceertain thats the version I heard, although the 'servant missing the plank' bit I definately remember.
Live the vocals were a little coarser as well, I'm sure;
"But better you make it extra large, or you won't get
him all in."
was
"But better you make it extra large, to fit the b*gg*r in"
Edit - checked the Kippers web site, so it must be right!
