In 1973 he finished second in the Production race on a Triumph, entered by Boyers of Bromley. I think the incident you refer to was a practice crash that same year
Yes it was the Boyer of Bromley Triumph the front tyre either failed or had a very rapid puncture and came off the rim, think he hit the kerb.
The man could not be found at first, John was catapulted a great height into the air into tall conifer trees which broke his fall onto someones front lawn it was just after the flat out right hander after Ginger Hall with a bit up of a front wheel lift (in those days).
You could say he stopped at the location rider okay.
At a bit of a loose end this Christmas are we Pykey?