Brooklands: I think the point of the video was that proper cross-checks of the glideslope vs. distance should be performed (especially in the third world where signal integrity systems may not be installed or ignored if they are). Whilst Cranfield doesn't have a DME, when performing an on ILS RWY 21 you should be at 1,560' when passing the (L)OM and 640' at the MM. These two checks will give an indepenent check on your G/S performance.
PM