I suspect it depends somewhat on the Inn that interviews you. That said, I don't know that determination generally is enough - I recall being grilled quite hard on how I knew I wanted to go to the Bar; they don't want to give you money and then see you run off to a law firm.
It's worth noting that, generally speaking, you can walk into any court and watch. I'd recommend a trip to the Supreme Court, as you can look up in advance what the cases are and read the judgments in the courts below to get a feel for what's going on. There's seating for the public at the back. I might be tempted (although I never did) to go to the Old Bailey too, as the advocacy will be completely different and will give you a contrasting experience to talk about.