Hmm okay, so I tried setting the first flight to UL instead. This produced a fare which was about £400 cheaper. I assume it's airport taxes or something. Routing me via Melbourne instead of KL.

So I've gone with that and the system produced a number for me to call in Sri Lanka. So far so good.

Now it wants me to call the SriLankan Arilines Global Call Centre 94 77777 1979 to arrange payment. Has anyone done this before ? Do they email you a payment link or something ?