I had my interview in March 2009 in the office of my interviewer. The Alumnus graduated in 2005 and works in a multinational company specialized in M&A. LBS interviews are non-blind interviews, therefore the alumnus has carefully read my application. Hence, when we started, he told me not to repeat what I had already written in my essays. It is important to be prepared with alternative and interesting stories!
He focused on my background and work experience (heavily quant) and why I wanted to pursue an MBA vs. a PhD or a MSc in Finance. Then, he asked if I could fit well at LBS and how I could contribute to the study group. After more than one hour talking it was the part of the impromptu presentation (now compulsory in every interview), it was something related to the current crisis, and therefore not too difficult to handle.
Last 30 mins were devoted to my questions. I asked him a lot about his experience inside/outside the classroom, how the MBA helped him in his work experience, which clubs he joined.