Originally Posted by
MSPeconomist
Maybe the OP needs a good real live human travel agent to piece together the desired flights. There will probably be a ticketing fee, but doesn't BA impose a phone ticketing fee too? If BA interlines with the nononeworld carrier, it can be on the same itinerary/ticket, although there can be restrictions in the fare rules about what fares can be combined, so that complex itineraries sometimes force higher fare classes than what inventory is available.
Yes the last part is certainly true, in this case W may be the required booking class to combine if another carrier is used - this could be even if its simply a non BA flight not just if its a non OW carrier.