I doubt the twin exhaust did much but the silencers seem to be special items. Ariel club could not say what it was as they had not seen those silencers on any bike.
It was a Red Hunter 500 though for certain.
Also used on hillclimbs on muddy surfaces. They were just ridden bikes back then. No trailers.Here is another of his bikes from that era. He was a Coop insurance agent and used bikes for normal transport