Near the end when they are about to load Mr Bluett in the van, Hodges opens the door and hit the side of the van twice making Jones pull away. This was filmed in the studio. Everything after was filmed on location. However, the blanket that Mr Bluett is under turns 180* (due to stripes on one side) from studio scenes to location scenes.
When the gas starts leaking Jones and Walker start giggling. But the van wouldn't have been using laughing gas.
When Jones first gives out the extra sausages, the women start talking among themselves. Right afterwards the camera returns to Jones and you see the shadow of the boom mic going over Jones's hat.
At 27.28 and 27.37, a TV aerial is seen, along with a concrete lamppost with a sodium fitting. There was not TV outside London until after the war, and sodium lighting didn't appear until then either.
At 25.17 and 25.22, a boom microphone can be seen in the top of the screen.