Those old enough to remember will recall that when Donegan made the now classic version of the song, "Nana" was a slang term then popular in the UK. I suppose it to be an abreviation of banana and a word close in meaning would be "Twit." Perjorative, but in a teasing way. It may be that "Nabob" was as originally written by the composer but Donegan interpolated "Nana" to give contemporary relevance and meaning - compelling evidence indeed for the mans genius and grasp of zeitgeist. I also recollect that at chucking-out time at a pub in Richmond, Surrey, the landlord was becomming extermely irritated with customers disregarding his cries of "Time. Please" and not getting out of his pub and as he became more insistent a young Irishman stood up with his guitar and belted out "My Old Mans a Dustman" - most gratifying.