IIRC the PVD resulted from research by the Blind Landing Experimental Unit (BLEU) in conjunction with Smiths Industries and Hawker Siddley for use in the Trident aircraft. I assume that BA (BOAC/BEA) provided some evaluation crews.
Further research included vertical guidance – see the installation in HS 748 G-ASJD (later XW750 BLEU)
HS748 G-ASJT - a photo on Flickriver
There was also some later research using LED dot matrix systems for flare guidance.
Also IIRC, the military considered some applications of the concept for low altitude roll attitude awareness with a strip display around the windshield.