Another idea would be to fly CX to London. They have three flights to London at or after that time so you can get a bigger margin for error (and enjoy their lounges if you have access), you will get miles and points (on eligible tickets) as they are oneworld partners, they are rather more likely to take care of you if things go wrong, and IMHO the hard and soft product on board are just so much better than BA (well, maybe except the food, which is much of a muchness)