Quite right Midman. Pilot's Notes for the Lightning T5 state (as amended in 1973):
"During an ejection attempt, if the canopy fails to jettison after both seat firing handles have been pulled, it is likely that the canopy jettison system is faulty; in this event use the normal opening handle to remove the canopy."
That's an awful lot of lateral thinking to be done at low altitude with faltering controllability, and with no Duty Pilot in the tower with all the books on hand and able to offer instant advice.
Rest in Peace David Stock; you will not be forgotten by the Lightning fraternity.