Great Portland Street was of course the next street along from Broadcasting House, where he was went he made the remark. He was the first in "Just a minute" to go the distance, and I think the subject thrown at him on that occasion was Diogynese. (He was something of a classics scholar, and heavily into Gibbons' Decline & Fall.

Would not have been able to recall those Rambling Syd lyrics, so thanks for the memory. But a line or two from his camp creations Rodney and Charles always stuck in my mind:

"Hello Rodney"
"Hello Charles."
"How's your bottom, Rodney?"
"Shut up!"
"So's mine. Must be the weather..."