Submitted my CV, did Situational Judgement and Deductive Reasoning Tests. Then they invited me to an interview in London. It was with three people (an analyst, a principal consultant and a director). It was about 45 minutes long. They asked about my interest in the role / industry and some maths questions. I later found out that the other interns at Aon had to go through an assessment centre, but GI doesn't do this (for both internships and graduate roles, they only have interviews).