Hi rho
I'd be happy to share my experience. I interviewed with one of the admissions staff in the US. He thoroughly read my essays and resume, so I would recommend that you know your own story inside and out, as he/she will grill you on it.
You should be very prepared to talk about why Oxford and how the program will help your career. In particular, I was grilled on whether i wanted to work in Europe and whether I was aware of how tough the immigration rules are right now. Though for you, looks like you are in London, so maybe that's not an issue at all.
Be confident but not arrogant. And be very honest. I was asked what one of my failures are. And I talked about how when i was very young, I lost a full scholarship to my school because I just didnt go to class and how hard the journey to climb back up was. Dont be afraid to admit mistakes, but always be prepared to talk about how that made you better and what you learned from it (and what you did to rectify the situation). Be prepared with a professional failure story, as they will likely ask that.
Whatever career you are going into, whether its a switch or a continuation of your current career, make sure you know the industry very thoroughly. Prepare a few targeted companies that you would like to research and work for, as they would be interested in knowing whom they should target as well.
Hope this helps. And good luck!