Would cutting a live gas pipe with an angle grinder be Riddor reportable.
It could well be argued that a gasleak was created by poor workmanship/illegal gaswork. This would be a riddor case. For a one of case, they could probably talk their way out of it,but a few repeats could well lead to prosecution. I doubt that the builder would have enough knowledge or the rules to dodge them, but his mate might know how to do it.