Very nice, first saw this on the Cascao "sweep the world" series but haven't had much luck with the initial step of blocking the far leg with the inside leg. However, in your competition footage I see that you managed to get your back leg hooking uke's far leg *before* trapping it with your inside leg ... gonna try that.
Loving your YouTube channel Lachie
Especially the half guard underhook combo. It's something I've used for years, but all the little details made a big difference.