Well it didn't look that unscripted to me. Much of it was interacting to the radio which is a bit of a con especially as it had so much of the episode. The radio sections didn't sound just randomly live, it sounded selected, with that long monologue about trannies. If it wasn't randomly live as they turned it on then the episode wasn't unscripted.
Also their reaction seemed quite muted as if very conscious of the fact of being filmed. There wasn't a lot of true spontaneity about it imo, which had me thinking this was either a second or third take or even edited, both of which would not qualify as truly unscripted in my book. I don't know how much a part the car radio plays in normal episodes as I've only caught about half an ep before this but don't remember the wireless playing such a big role as it did here.