UGSAS
Right well firslty well done for gaining an interview. The first informal chat you have before te interview is also a screening out point.
The interview will last about 45 mins. There should be two people undertaking your interview.
Section 1 - Is all about you. Starts off with "whats your date of birth" questions and "so how old does that make you in years and months?". All to put you back on the ball again.
This section is all about you. Your family, your home life, you education, you in school studies, out of school interests, exam results.
This section nothing of great weight shall be said about RAF itself.
Section 2 - Is all about the military side of the interview.
It will focus on your knowledge of the RAF, equipment, weapons, squadrons, stations (overseas too). Will ask you about out the UAS fits into the wider picture of recruitment for the RAF. What aircraft will you fly - pressuming you pass the medical - if you fail this selection what will you do?
They will also probe your knowledge of current affairs. They could say "take me around the world using news headlines and briefly explain to me 6 or so topics that have occured in the last 12 months that have interested YOU".
Any questions - this is tagged on at the end, don't ask anything silly like "i know the competition is stiff so what are my chances?".
Hope this helps, and good luck. Oh and there may be current students milling around helping - my tip - don't let your guard down will you've got a place.