Thanks everyone for your replies. Most informative !

So if I understand correctly, if I look up a paid EI flight on ITA the taxes and fees displayed will more or less match the taxes and fees charged on an award itinerary using BA miles ?

Is there anything to prevent me from bypassing LHR completely, and booking something like CDG - DUB - ORD ? Assuming availability of course.

( Runs away to begin lobbying EI for a weekly SNN to YQR flight )