Faint memory: Stansted airport airshow

[Tony1963]

I’ve had a Google etc, but can’t find any info.
I’m guessing somewhere between 1969 and 1973, an airshow at Stansted, but all I can remember is climbing through a hatch in the cockpit ceiling of either a British Air Ferries or Transmeridien aircraft and watching the day’s proceedings from up there.

Does anyone know more?