Similar wording to curvedsky's quote can be found in the Pilot's Notes (Part 1 Chapter 12) for both the F6 and the T5 at the end of their RAF service. Some words are subtly different compared with the early F1 sample above ("interdictor" for "restrictor", and "canopy" for "hood" in the 'NOTE' line), and the times have changed (F6, canopy depart to seat fire is 0.6 seconds, on the T5 it is only 0.4 seconds).
The 1973 amendment to the canopy jettison procedure, which I quoted in my post above, appears in Part 1 Chapter 9. BOAC is right; if the 1966 accident was the reason for the amendment, 7 years is an awful long time. Could there have been another accident in the early 70s, when someone ejected successfully after a canopy stuck and they got rid of it by using the normal operating handle? I am afraid that's a few years before my involvement with the Lightning began, but somebody may remember.