Originally Posted by Sean Dell
can we make sure that we intercept the loc before the glide
The ILS is a precision approach. Descent should not commence until established on the localiser. Heathrow directors will ensure that aircraft are established localiser before issuing descent on the glide slope. Heathrow directors will ensure that the GS is captured from below and to do this a couple of miles level flight is normally involved. Then you can do what you have to do to with gear and flaps to get the trim change you need for the stabilised descent at the standard speeds.
The expectation to capture from above is poor ATC and I cannot believe that was the intention. Methinks you encountered the GS at a non-GS intercept altitude and asked to follow the glide before ATC could accommodate a GS descent. The procedures are constrained on westerlies when London City airport is active.