JEM60
I'm sorry to say you are right; although I was at school then,( 1974 ? ) my father was at Dunsfold at the time.
The HS125 was indeed demonstrating for a Chinese delegation; it had a bird-strike in both engines just on take-off, and John Cunningham did very well to put it down straight ahead - across the main A281 road to Guildford - gear up.
They all got out unscathed, it was only later that the fire crew found bits of car - the wife & children of one of the comm's pilots had been viewing at the end of the runway...
He is a very well regarded pilot, and I will not name him here.
After that the option of take-off run was changed, ( with the prevailing SW wind most a/c took off the other way anyway ) and raisable barriers were installed at each end.