Regarding Big Al Whittle's "I think it was John Peel who said he'd try anything once, except incest and morris dancing."

I have heard the quotation “You should make a point of trying every experience once, excepting incest and folk-dancing” (and variations on this) being attributed to many people, such as Sir Thomas Beecham, Oscar Wilde, George Bernard Shaw, Noel Coward ...
One candidate is Sir Arnold Bax, who included it in his autobiography Farewell My Youth, quoting ‘a sympathetic Scot’. But then, maybe this Scot was in turn quoting someone else.