2x 30 min interviews
Interview 1: motivations, problem sheet style question; Interview 2: physics and maths questions
Explain your thought process; review course content.
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: 2
Skype interview: No
Length of interviews: about 30 minutes each
We talked about why I wanted to study engineering, and I was given a question based off of that. Then, I had to do one problem sheet style question that built up in complexity.
In the first interview,
The second interview consisted of more basic physics and maths questions, very similar to high school. The atmosphere at this college was much more friendly. The interview was conducted on sofas in front of a fireplace. I relaxed more, but not much more.
I did the practice papers on the uni website.
They're looking at your thought process, so explain every step of the way and be prepared to explain why you think your reasoning is correct or where it might be wrong.
I didn't prepare for interviews, other than looking at the example ones provided by the University (i.e. the physics one). I entered with very low expectations that I would get in (and thinking that I'd mistakenly gotten an interview) so I just enjoyed the process.
The best thing I did wasn't on purpose - I happened to be revising for mocks at that time, so all the knowledge I could've had was stuck in my brain.