Michael Bell writes:
But I think I remember newspapers reports that at one time London
Transport were REALLY thinking of 3-decker buses. Anybody know anything
about it?

No, but Heath Robinson once did a cartoon showing 3- and 4-decker buses.
The title was something like "Some suggestions for improving traffic in
London", and it used to be -- perhaps still is -- available as a poster.
--
Mark Brader "Inventions reached their limit long ago,
Toronto and I see no hope for further development."
-- Julius Frontinus, 1st century A.D.