Create a Character Style in InDesign that consists only of the Bold attribute. Import your Excel document as a formatted table. Once your table is in place, use Find/Change to apply your Bold Character Style to the bold text from Excel. Once that is done, you can apply Paragraph Styles to the whole text without losing the bold from those items.
Thanks for your reply. Not sure if I've been clear enough with my question - my problem is that when I import my excel document into Indesign it loses all of the bold formatting that was in the Excel file straight away. Even if I import it as a formatted table it comes through as just plain Times New Roman, with no lines of bold text, so I can't use find/change to identify the bold text as it doesn't appear to exist once the table has been imported into Indesign. Does that make sense (not sure I'm explaining it very well, forgive me)?
Are you able to share a portion of your Excel document through dropbox, or another file sharing service? I use this method to retain color in Excel charts, placed into InDesign, so I may be able to see what is going wrong.