Young aviators might need reminding that there was no RA (radio altimeter) on VC10s (unless the BOAC/BA a/c were doing autoland trials - finncapt?).
The height difference between the pilot's eye and the aft belly fairings in the flare was greater (even on the standard VC10) than on other narrow-bodied jets, so this would have been a fine bit of visual judgment, particularly as it was over a short, grass runway.
Yes, Alan Harkness went on to have a distinguished career in training and management.