Step 1: Online application with a timed quiz about solving numerical and logical problems (find the next number in a sequence, etc). You are notified by email if you passed this step and what happens next.
Step2 : Telephone interview (45 min - 1hour); very professional interviewer, pretty much standard stuff, why do you want to work for BA, what do you know about us, what did you do in the last two years, what do you know about the role you have applied for, what motivates you etc. Second part consists of competency-based questions: tell me about a specific situation when you had to deal with conflict and what did you do, or how did you improve a process. I was asked four questions and I was told that I passed at the end of the interview.
Step 3: Assessment day (approx 2 hours) at Holiday Inn Express, Slough, or other location. We were 24 candidates, in six groups of four people. In the beginning there was a presentation about the role, then each person in a group had to present himself/herself to the others (one assessor for each group). Next there was a role-play exercise: you receive a card with a specific situation. You have 4 minutes to think about it, then you need to read it to the assessor who will play the part of the client.
Last part is a group discussion about a subject (such as arranging in order the most important brand values of BA). The assessor will listen but will not intervene.
Overall, you are assessed against the following competencies: resilience, customer service, problem solving, adaptable, energy & enthusiasm, reading ability. You are notified about passing or failing in less than 2 weeks.
Hope this helps.