Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
"And either way, am I correct in saying that there are no BA flights from the US that don't go through London, so the only way to use a companion ticket is to pay the high fees?"
Yes, assuming that you want to use the companion certificate from the U.S. (And it may be that your companion certificate is only valid for award itineraries that begin in the U.S. Check the terms and conditions to be sure.)