The first stage was applying with your CV and cover letter. If they accepted you then, you had to answer questions online about the company and your strengths and weaknesses etc. They then ask you which specific sectors you want to be involved in. If you pass this stage, then the next stage is asking specific questions about that sector. This is done through an interview website such as HireView. The final stage is asking you to come down to London for an in-person interview.