I would suggest three centres. One in UK (obviously), one in Australia and one in North America. Have sufficient staffing levels at each and you cover the globe while minimizing night extra pay.

That's my armchair solution to this. Of course there's more to it and BA most certainly have reasons for what they're doing. I do appreciate that BA strive to offer service in many languages


On an aside
What's funny when I call the line in the Netherlands, even though I choose Dutch, more often than not I'm helped in English by someone in Bremen. If I'm in a good mood and the person has a heavy accent, I'll even switch over to German with the agent :-)