Around the time skiffle was taking off in England and Bill Haley and the Comets were rocking around the clock, two men went on stage in a west London theatre with At The Drop of a Hat, a collection of funny songs they’d been writing since they were at school together. It was an instant success, with the witty wordsmith Michael Flanders declaiming from his wheelchair while at the piano, looking slightly daffy, was Donald Swann. Over the next decade...