Thanks for the replies, but I am unable to even select the particular flight as there is no button showing - I wonder if it is because it is showing the BA codeshare number, rather than the CX flight number. I've tried it on 3 different browsers, so it isn't a browser problem. On the BA website it doesn't even mention selecting seats on the CX or QF flights, but I can select the seat on QF on their website, just not the CX ones