Yee*hah*: Now I know where Denis Norden got this from. When he perpetrated a condensed version in a late edition of My Music, he claimed it couldn't be found on the Web, which led me to think it was a WW2 parody (presumedly from the British Air Force). He only sang one verse, of which the last two lines were:

Are your dentures so worn, they fall down when you yawn?
It's no wonder you're ....

.... at which point he (and the piano) got drowned out by the audience's laughter and applause.

I shall add this to my repetoire when Herself isn't around.