Nick - my apologies, your answer was spot on. The trick is to use your
GetSaveAsFilename, in preference to my FileDialog(msoFileDialogSaveAs). This
doesn't show a "do you wish to replace" query, hence the message on SaveAs is
the only one! All I needed was

Dim Retval As Variant

With Application
Retval = .GetSaveAsFilename("C:\Temp\Test.xls")
If Retval < False Then
ThisWorkbook.SaveAs Retval
End If
End With

Simpler code too. Many thanks!
MattM