Whenever there’s a debate about the merits of high visability clothing and daytime running lights, someone usually claims they know a “friend” who has made an insurance claim due to an accident, but their compensation payment was reduced due to them NOT wearing hi-viz gear.
But the facts are that motorcyclists are simply required to take reasonable care for themselves.
There is no statutory requirement to wear a hi-viz jacket and therefore no Court would make a finding of contributory negligence for the failure to wear such a jacket.
If the third party’s insurers tried to suggest that, any half-decent lawyer would kick it straight out. If they didn’t you’d need to change solicitor pronto.