It was a rather poor process a couple of years back in London. Having gone through the various stages of writing samples and multiple partner calls that are conducted over teams and mobile, often with their US offices, it was a real letdown. Once I reached the final in-person interview in their office near Liverpool St, it consisted of an entire day of interviews in which they had another candidate interviewing at the same time - Having poorly organised the day I was forced to wait for 45 minutes in the lobby so they could cycle the chats between the Partner, the Principal and the consultants in good enough time (shocking for any professional services company)
Once it finished it took them over 5 weeks to respond to me about the outcome of the final round which is not only disrespectful but just morally wrong for an employer to waste so much of your time. Even when you have been through these 4-5 stages and waited over a month to hear about the outcome of your final round you're not even given the slightest detail as to the reasoning/ position they hold about your application. Strongly advise you to avoid this firm.