What Nadia wants to hear are the chimes of big Bill, but that is a mistake, "big Ben," No.6 corrects her, and Nadia will never call him anything else. "Goodnight Nadia" "Goodnight big Ben." "Big Bill" Number 6 corrects her again.
My wife is of the opinion that Patrick McGoohan would rather enjoy being called "Big Bill!" But I have always seen this as perhaps an unintended reference to Bill and Ben the flowerpot men!