Hi James. Congratulations and welcome to the forum! Personally I've no experience of an interview for this role, but generally I would say to make sure you look smart, maintain eye contact, think about responses before you give them, speak clearly and try to relax. The fact that you have reached this stage shows that they are already interested in you!
In terms of answering scenario based questions, use the STAR approach. Tell them the
Situation
Task
Action you took
Result
Hope this helps and good luck!