Have resolved the issue but thought I'd post solution in case anyone
comes across this in future.

I had erroneously added an unnecessary reference to the Project (in the
application) "Lotus Domino Object" (which was originally used for E
mailing a response back to the centre, but code changed to late binding
when early wouldn't work).

In Excel 2003 the superfluous reference caused basic functions such as
UCase, Right, Left etc not to be recognised.

Simon