Multi-stage interview process: stage 1 was a phone-based interview with someone with a similar level as the role I was applying for which consisted of an experience overview of what I had done in my current role, and a case study section consisting of what considerations to take care of from a technology perspective when doing technical due dilligence on a potential acquisition.
The second round was an in-person interview, much along similar lines, except this one had the case study swapped to talk about what technology considerations to go through when evaluating a merger for a client.
Most of the team for this group of BCG is not based in UK, so interviewers were from their other European offices.
Overall, I got the impression that the team primarily still worked in a fair amount of traditional M&A / IT transformation space rather than anything in new technology.