45 years later, there's now about 28 direct services BKK-LON per week.
Truly an impressive growth rate !
Not a fair comparison: the 28 direct services are nonstop. Back in the day, aircraft couldn't do the long sectors unless virtually empty and there were not enough pax for such a sector because of comparatively higher fares and only richer people (and airline staff) travelling), so sectors were linked together as a matter of course.
Also, because of the cold war and a prohibition of overflying the Soviet Union and China mainland, it was neccessary to the go long way round via BKK and BOM.
AI, a top-notch carrier in those days, (hard to believe perhaps!) took full advantage of being half way between Europe and Asia/Australasia on this "long way round" and channelled pax through its hub at BOM, sometimes without even a change of aircraft.