Nuts! So that means all the African destinations only served by BA are off-limits for the British? Unlucky. Thanks so much for the quick response – sorry I wasn't able to figure it out myself.

I suppose I could try to do the same sort of plan ex-Spain or something like that, but not only does that add more bother around Christmas time, but the savings from buying it in Euros is nothing like from buying it in pounds. Looks like I may just have to drop the plan (and CAI!) and buy LAX-BRU-EBB-BRU-LAX-NRT-LAX which comes in around $3000. What a nuisance!

Edit: Or maybe an overland segment could come into play here? Depending on the cost (and I haven't looked into it) maybe an EBB-JNB separate flight could get me back on track, as then I could take IB through MAD and then on to CAI. Or simply EBB-CAI on EgyptAir?