I remember one of their songs was arranged so that one of them sang a verse and the last three sylables were repeated, music hall style, by the other. I can't remember any of them now except the one they changed. "Upon that far canal" had "fancy that" sung after it

I can also remember that. I think it was a parody of a Gilbert & Sullivan song, but I can't remember which. It appeared on an LP of some musical highlights from the TV show, but I was disappointed on hearing it to find that the verse with "far canal" had been edited out of the record. I assume this was for space reasons, as I can't imagine why they would have removed it on taste grounds, since it had been broadcast at peak time on BBC TV in the 1970s.

I probably have a tape of the incomplete version from the LP, somewhere, if I can find it.