Simple, the B777and A380 were on my list of tolerable to fly long haul Y class. The B787 was on the intolerable list, which now includes 10 abreast B777's.
Anyway, seems Qatar have relented and offered BC home from Europe for a little less than the half the original BC return fare (including the unused part of the Y class return fare).
Still leaves me wondering how one buys two seats for one person, apparently not an unusual situation.
Thanks to the contributors to the thread who pointed out the intricacies of Y class fares (and some aircraft types which may be tolerable), I realize that it is only luck that I haven't previously been caught out - over very many years of long haul air travel.
Last edited by zzuf; 21st Aug 2017 at 10:30.