3x 30 min interviews, over 2 days
Interview 1 (philosophy): personal statement; Interview 2 (politics and economics): abstract politics question, economics problem
TSA solutions bok, practice papers
Look at past PPE interview questions and have internal discussions in your head.
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.
Number of interviews: 3
Skype interview: No
Interview spread: 2 right after one another, the other a day apart
Length of interviews: usually about 30 minutes each
In my first interview, I was asked why I was interested in PPE and philosophy in particular. There were 2 interviewers, who put some emphasis on my personal statement, including literature I had read, and we had a discussion over the merits of a particular philosopher and his ethical viewpoints. It was relatively chill and with a friendly atmosphere no doubt driven by the interviewers themselves.
The politics and economics interviews were much harder. Abstract political questions were asked for a meaningful discussion with the politics interviewer, and right after was an economics interview that consisted of a problem on the board that we were asked to solve. I was helped through the problem at times by the interviewer if I got stuck, which sometimes happened due to its difficulty, but the problem itself required only basic prior knowledge of economics, and mostly tested your sense and quantitative ability.
Some easy advice is to look at past PPE interview questions and have internal discussions in your head: the more the better. Most will not actually come up, but if you have seen many questions of that calibre, you will at least have a solid idea of what you can expect from the interview and avoid being as nervous.