I have never seen that film before. Obviously made at Hythe, at the Small Arms School hence SASC on the shoulder titles there (SAS on the rear of the 15cwt truck). If my friend Maurice Fogwell was still alive, he could have identified the identities of the men in the film,. Sadly, he's gone. Anyone get the serial number of the early original Mk1 gun. Notice the 'safety stop' on the early barrel nut.
added later..... Ruptured cartridges requiring the use of the clearing plug wasn't a big problem with the .303 or 762 Brens because the case wasn't snatched from the chamber. Rather, as the breech block tilted upwards it levered the case from its locked taper. Primary extraction in operation so extraction was a gentle tweak followed by a violent ejection. So violent that if it wasn't for the hefty oval punch that sealed the primer into the case and (on the .303 gun), the stake mark by the ejector that reinforced the punched and expanded primer, the Bren would suffer from stoppages caused by detached primer caps clogging up the mechanism