That is the Finningly one. Pax drills was probably a question of availability. If you were at Finningley, or there was a trainer, then you could do the drills. In the end we seemed to get so many guests that we ended up giving a standard 'airline' patter and simply took their word that they understood.
As we had to fly with Iranian officers I guessed that they would say yes to anything so I wrote out a comprehensive brief - no smoking, no guns etc - and we got it translated at the Embassy. It was on the next flight after the brief was introduced that a Vulcan crash landed.
I am sure it was a great comfort to the observer to know he had taken part in an 'extremely unlikely' event.