Imperial Business School has a slightly different approach to the MBA interviews. There is a 30 minute discussion with a faculty or a member of the admission committee, which is followed by another 30 minute discussion with a staff from the Career Services Department. This clearly helps your discussion segregated into "you-as-a-person" and your professional goals.
The interview with the faculty / Admission committee is typically very informal, and you'd be speaking about your current / past job, hobbies, etc. Although, you might end up talking about why MBA, why this school, sort of questions as well.
The tone of the discussion with the Career Services staff is formal. In all likelihood, the starting question would be on your post-MBA plans. Your understanding of your desired job role will be gauged with questions such as: What skills and traits you think are essential for your target job role? How would the MBA help you gain those? Specifically, how you think, would Imperial help you gain those?
Of course, this list (if one can call it that) is indicative. And, given the (hopefully) two-way nature of any interview, your next question depends on your last answer