I had one interview and then a case study question. The interview was comprised of half competency based questions (why Barclays, why marketing etc) and half situational (tell me about a time when... what would you do if...]. It lasted about an hour. The case study, you are given 10 minutes to read through a deck, and then 15 minutes to present back. I would recommend making yourself familiar with their marketing strategies and key public policies.