"He'll have to learn melodeon for the part" - see Hamish's comment 12.10.11. My thoughts too, so when I saw Bob Fox at our local folk club just over a year ago, I complimented him on his playing and learning it so quickly (took me years too!)
"Ah" says he, "I only know that one tune - just learned that one - can't play anything else"! What a professional!

I saw the show a few years previously when Bob was Songman: best piece of theatre I have ever seen. had to resist the temptation to join in with the songs, all of which I knew, being surrounded by various unknown people who might not have appreciated that!