Here are some videos from early sessions. They mainly consist of making really stupid noises. Beatboxing takes lots of practice. This is something I've learnt from these sessions. Also, you often get very lightheaded and need to drink a lot of water otherwise you feel like you're going to pass out. I don't know how they do it!
Here's a demonstration of what the Beatbox twins can do:
And here's some of our participants! Farzan at Naseby:
Younus and Forid at Hutton: