Process took approximately 4 months between application and offer. Overall a positive experience with enjoyable interviews (as far as they go). Only downside was poor communication from the recruitment team. I had a particularly long wait between final interview and offer (around 6 weeks after a promised turnaround time of 2 weeks). Perhaps I was unlucky but I would say be prepared for long periods of no contact due to recent increased recruitment activity. Process outlined below:
1) Form and cover letter
2) First stage interview at London office; 1 hour, one-to-one with a manager, mainly focused on going through and discussing CV, some basic "tell me about a time..." questions, very relaxed, not hugely testing - just checking you're suitable for the next stage
3) Final stage interview (took a while to arrange); 2 hours in London, 2 interviewers (one more senior than the other), asked to prepare a 20 minute presentation on a complex problem of your choosing (testing your presentation skills and how you can tailor a topic to a certain audience), asked some challenging questions on the presentation, a deeper dive into your CV and experience, questions on why you're attracted to consultancy, general discussion around suitability for consultancy, one "unseen problem" which is designed to test how you think (just work through it logically, make any assumptions clear, use the board for your workings), very nice interviewers helped to make my interview fairly relaxed and conversational