Maurice,
I don't quite understand why the standard Data Validation
using a List will not suffice as this (can/does) prevent entry of data not in
the DV list. Am I missing something or just dumb?

The validation is there; whenever the user types something into the cell on
the keyboard, the input is validated against what is in the list of the
cell's dropdown box. Anything entered that is not in the list is rejected.

What I want to do, however, is to reject any and all keyboard input into the
cells with the dropdown list, before it is even entered - and thus force the
user to make a selection from the list using only the mouse.