WHBM
Thnaks for your kind answer I certainly remember somewhat telling me it was JAL route proving and clearly was DC8 then CV880 and back to the Dc8s, not much difference in smoke from what i assume were DC8 -30 series
And back then of course London-Tokyo was not long hail just a series of short /medium haul sectors stitched together. used to love the timetables from those days like a bus timetable with all the city names it stopped or missed according to days of the week, very exotic to a ten year old .
thanks again