First you will go through a phone call screening process where they ask you basic questions to see your base-level technical capabilities and see if you would be a cultural fit. Once they decide on an in-person interview, you will be in a room with local middle-management and 2-3 Senior London/Manchester Engineers / Managers. Each will take their time asking you questions (often they make them far too hard to see how you will go through the process of figuring it out). The interviewers are almost always very friendly guys and while may appear tough at first, they will be very understanding so long as you are honest and yourself. I would suggest bringing a sweater as they like to make the interview room too cold to put you under 'pressure'.