I'm a retired design engineer, much of my time was involved with HV power systems at the industrial level, and HV distribution systems in the middle east.

I have no professional association with CEGB, but in my early days as a design draughtsman, worked on the 400 kV supergrid when working for the consultants Preece Cardew & Rider.

I email in the hope someone will recall a large power outage across the England, sometime in the late 1960s or early 1970s. As I recall it this outage was nothing to do with a shortfall in generating capacity, but a cascade of nuisance tripping on the supergrid following the clearance of a system fault. I believe it later transpired that the system protection settings were unstable under certain conditions.

If anyone can remember when this incident occurred, and provide anymore details I would be most obliged. I am currently writing an essay on security of supply and hope to cite this incident.