I know surcharges on IB and BA suck, and LHR is bad; but which is worst? I can go SCL-LHR on BA, or SCL-MAD on IB ... mind you the ultimate destination in Europe is KTT (can't use my OWA as I'm short of allowed miles), so at least LHR is slightly closer and cheaper for a cash ticket ...
Not so sure about surcharges but the business class experience on IB will be better than the cramped business class seats on BA.