First there is a very difficult online test. Then, if successful the company invites you to their offices in central London for 2 interviews (one CV based and another one case based). I didn't get selected to the following round which was the final one. The company is very helpful though, they provide every applicant with a buddy to ask any questions about the firm and they also provide feedback after the interview.

An online assessment (Math and Behavioral) followed by 1 group HR interview and 3 case interviews. You have to pass each case interview to move into the next one. Cases mainly focused on market sizing skills.