Here is the Precision Approach Terrain Chart for LHR 27L:
http://www.caa.co.uk/docs/64/DAP_ACD...ow_Rwy_27L.pdf
Note: The elevation of the runway is 77 feet AMSL. Elevations in feet - All other dimensions in metres.
The ILS Glide Path is aligned to give a Threshold Crossing Height (TCH) of 56 feet.
From the chart you can interpolate where the aircraft should be at 600 feet on a 3 degree glide path.