2x interviews
1st: problem solving, personal statement; 2nd interview: biology based
Mock interviews help with articulating academic thoughts
Bring a book to distract yourself pre-interview
Remember this advice isn't official. There is no guarantee it will reflect your experience because university applications can change between years. Check the official Cambridge and Oxford websites for more accurate information on this year's application format and the required tests.
Also, someone else's experience may not reflect your own. Most interviews are more like conversations than tests and like, any conversation, they are quite interactive.
I had 2 interviews both on the subject and both with 2 professors interviewing me. The first was more laid back with more open questions while the second (about 2 hrs later) was perhaps more formal with one of the interviewers
As some people have never studied psychology, I found that the questions were more to do with ethics at least in the first interview. I was asked one very open-ended question on my personal statement. I was given a scenario and asked about the ethics of the situation. I also jad to interpret a graph and give the implications of it and answer a brainteaser-type question. The second interview included questions that were more biologically based and included constructing an experiment.
Bring a book (or something non-psychology related) to do before you go in as you will be sitting in a room with a lot of other people. Personally I didn’t talk to anyone else which suited me as I overheard conversations about how much work everyone had done which can be rather offputting.