First, you would have to submit your resume at Jobs@BAT. That's the only way to apply.
Then, there would be an initial CV screening by a designated team. After checking the hygiene qualifying parameters, this team primarily looks for leadership evidence. This is of paramount importance. Your resume would never make it for an interview if you do not include extracurricular experiences - leading small groups (football, cricket, debate anything helps).
Then, if you qualify, you'd be invited to a Primary Interview (PI). This would be done by one or two Certified BAT Assessor(s). In a one-to-one close door 'Hard Talk' type interview, the interviewer(s) would want to know you as a person. What's your leadership style, how you have dealt with stress, challenges in your life - in professional, student, personal or social settings. If you face this interview, in answering the questions, be as specific as you can. For any question, instead of giving a number of examples, try to stick with just one example. And, share very clearly - what you personally did in that setting, what was your own contribution, why it was so important and so on. Try to get exactly what is being asked and answer that very well.
If you pass this stage, then, you would be invited for an Assessment Center. A whole-day event where you would be taken through a number of exercises (usually three) with a number of other candidates (usually, six to eight). These would include Group Discussion of a Business Case, Fact Finding or Role Play and, finally, a Business Presentation.
Next, in another day, if successful, you'd be asked for a Final Interview. This would be with a Senior Manager - typically, the Head of the recruiting Function.
And, finally, there would be medical check up :-)
All the best!