The answer to the Pub Quiz question was: A and B road designations were created in 1920.
I can't find a web reference for that fact, but it must be true because it was on the Chris Moyle's show a couple of weeks back.
All this leads up to what promises to be an excellent programme starting on ITV tonight: Robbie Coltrane: B-road Britain.
It's a shame he chose a Jag to go round in. I would have thought a Morris Thousand would have been more appropriate!