At the risk of repeating what I have recently posted on n the ‘Sale Fares Discussion’ thread on this forum - select Netherlands as your country on BA.com and (my preference) type in a multi-city itinerary of AMS LHR SIN BKK HKG LHR AMS. INCEU60 rules charge, from memory, an additional EU100 per stop (more than 24 hours) - so ensure your stay in SIN is less than 24 hours. Your stay in BKK (essentially the destination for this fare) can, in my experience, be as short as an hour. The extra EU100 you have to pay is for your multi-day stopover in HKG.

As others have said, try and avoid the apparently crappy BA 777 on the LHR BKK route, and instead fly BA’s A380 to SIN (earns extra Tier Points). SIN BKK HKG is with CX (from memory, if you select CX712 - SIN BKK HKG you don’t even have to get off the aircraft in BKK).

I actually prefer to play around with itineraries on ITA before plugging in dates/times at BA.com.

You can search for more information on the FT BA forum.

However, above all else I prefer to fly QR!