Understand what is being assessed
Interviewers want to see how you think when you meet something unfamiliar. They are looking for curiosity, clear reasoning and a willingness to be guided, not for polished answers.
Know your own application
Anything in your personal statement is fair game. Re-read the books and articles you mentioned and be ready to discuss what you found interesting and what you disagreed with.
Practise thinking aloud
For STEM subjects, work through unseen problems while explaining each step. Get comfortable saying "I am not sure, but I would start by..." and sketching graphs or diagrams as you go.
Mock interviews with someone who will push back and offer hints are the closest rehearsal for the real thing.
Secure the fundamentals
Most questions build from A-Level material taken a step further. Fluent core knowledge frees your attention for the new idea in front of you.