Questioners are rumoured to be keen on candidates knowledge of the Oneworld Alliance and BA's franchiasse partners. Also an idea of BA's products' future products and a bit on the opposition. Most of this can be gleaned from the BA.com site.
Perhaps someone who has had an interview last week can confirm. I am sure they will ask 'What is the most difficult situation with people you have had and how did you resolve it'. 'What is your greatest achievement'. 'What can you bring to BA'. Best of luck.