Bill Hayles wrote:

On Wed, 29 Jun 2005 23:49:24 +0100, Colin McKenzie
I believe there was a time when a few route number suffix letters got
up to and beyond H.

Not since the Bassom era. Certainly, post-war, the highest was
406F, and that only ran on Derby Day. Plenty of D suffixes, a few
"E" and that single "F".

I was probably thinking of the Bassom era.

But there were enough suffixes in the early RM era for suffixes to be
more appropriate than prefixes for these routes.

Colin McKenzie