Barry refers to Dilys' mother as 'a left footer'. We know from elsewhere that she was not a Catholic but from a middle class Protestant family. Surely left footer is slang for a Catholic? It was always used to mean that.
Bizarrely, in most of Ireland a 'left footer' refers to the other tradition. Protestants refer to Catholics as Left Footers and vice versa. We would also say the other tradition 'kicks with the wrong foot'.