BA is too expensive to start with and I've not always found KLM/AMS to be cheaper from NCL (though AF sometimes is).
If you catch it right NCL-AMS-BKK business class can be had for £1700 (CI a bit cheaper but can't book a through ticket) but if not it's £1700 for AMS-BKK but nearly £2300 for NCL-AMS-BKK.
Just on principal, even if I could afford it, I wouldn't pay nearly £600 for a 1hr flight where business class seats are the same size as economy and often the food is identical so all you get for your money is getting on first which never bothers me.
It's a shame they don't let you book a through ticket using economy for NCL-AMS then busy for AMS-BKK.
In the good old days CI used to let you do that (using KLM for the NCL-AMS hop) but not any more.
They call it progress.