This is an interesting one. Notice The Life Guards drum horse, the shabraque is the back half of a First Life Guards officer (it's not 1LG drum horse, that was white) and the drum banners still have GR whereas the trumpet banners have E 11 R . Possibly being used as a rehearsal set while the new ones are being made?
I've had some interesting conversations lately with "the old boys" about the old Knightsbridge Barracks 1878-1965 (that's in the film)
Martin