I passed these interviews about 3 months ago in London - where are you? The HR interview is very typical, less formal, where they ask about your work history, leadership experience, all the generic soft-skills questions. They may ask how much you expect in compensation and where you want to be in 5 years.
The Case study interview is also very generic and mine was not as quantitative as expected, but I wasn't applying for FS so yours may be. Prepare to get a full A4 full of company's case info; you'll then have about 10 minutes to analyze it alone, and then the MD will come back and ask you to talk it through with him/her.
Hope that helps.