Ferguson was accused of stealing all his material in his Bing Hitler days (mostly from Gerry Sadowitz), to the extent that almost the entire comedy community turned against him. One particular Edinburgh Festival was very traumatic for him and probably resulted in his move to the States, where he became very successful, as we now know.
Oddly, he was supposed to be a quintessential Englishman in the Drew Carey show, only Brits seemed able to spot the awful cod Bertie Wooster accent, the Yanks bought it.
Why on earth he is a successful chat show host I have no idea. On stage he was as funny as rabies in a guide dogs home.