I asked to come back to this question as I struggled with it at first, and the interview panel did mention they often have people not able to provide an answer and appreciated that I did. I answered that I regretted a change in job, to help a former employer as it was not the right move for me, although arguably it was still the right move as it was correct for the team at the time.
I said I was a recent graduate and then went on to talk about my work and volunteering experience. I ended it by saying I'm a pretty big football fan (but my interviewer wasn't too bothered about the last bit). I probably spent most of the interview on this question, letting the interviewer ask questions about my answers before returning back to talk about myself some more.