The first thing to say about mock interviews when applying to Oxford or Cambridge is that you do not need to have had one to succeed at the interview. For instance, I did not have a mock interview when I applied. The universities also emphasise that the way interviews are structured as largely spontaneous academic discussions should limit how useful mock interviews can be.
That said, having a mock interview is clearly useful in terms of familiarising yourself with the interview format and the sort of questions that might come up, which could reduce your nerves when dealing with the real thing. In retrospect, I wish I had tried harder to get some sort of mock interview, by asking my teachers or by applying to one of the many mentoring projects 🔗 🌟 available when applying. These schemes, such as Zero Gravity and Slipstream Education, often offer mock interviews as part of their sessions, and certainly involve advice from students who have gone through interviews, so are definitely a good option for any prospective applicant.
It is worth emphasising that mock interviews are not magic as preparation, and you could gain the insights that they offer from other methods. InsideUni’s resources can be very useful to learn about the atmosphere of interviews and the sorts of topics that can be covered in them. You can search for interview testimony from students for your university, course and even college on the InsideUni Interviews page 🔗 🌟, where past applicants discuss what their interviewers were like and the sort of things they were asked. It is worth reading a few of these as each is just one person’s experience, but they can be very insightful.
To get a sense of the types of questions that might be part of your interviews, Oxford University has produced a list of questions 🔗 that they have used in the past, many of which might also be useful for Cambridge. While you will not be asked these questions specifically, so you shouldn't prepare and memorise answers for them, they should provide an insight into the types of questions asked. Furthermore, videos have been released of mock interviews by lots of departments in both universities, which could be worth looking for on YouTube. Some of the best examples are linked from our InsideUni course pages 🔗 🌟.
A lot of the experience of mock interviews is about getting used to talking about your subject academically ahead of the real interview, but there are of course other ways of doing this. Regardless of your other preparation, it is worth trying to talk about academic topics with your family and friends as your interview approaches. Of course this also applies to talking to teachers and participating in class discussions. If your school offers some sort of debating society, that could be a useful way to have these discussions
The final thing to say is that none of the suggestions made here are necessary for interview success. No matter how they prepared, every applicant will feel somewhat nervous before their interview. The most valuable preparation is probably to have spent some time thinking and talking about your subject in any context, and to have thought about potential questions relating to your personal statement or submitted work which you can. Nonetheless, it could be helpful to get a sense of the atmosphere of interviews, and hopefully this post has offered you some useful suggestions on that.