When Karl did a Quinssa night before he left he was asked that question. He said there were no rules or regs that precluded him from reffing us but he doubted that he would be assigned to Quins as a referee for several seasons at least .
Im think he was a touch judge for an Anglo Welsh / A League game last season ?..
I stand corrected! Could have sworn I'd read somewhere that there was a system for keeping refs' potential biases (conscious or not) out of the game. Seems it's more just a common sense approach. It would be pretty unfair to choose Karl to ref a Quins game for instance - the commentators, pundits, journos and opposition supporters would all be looking for moments where he gives Quins an unfair advantage, and so the game would easily be brought into disrepute. Makes sense not to put anyone in that position - which is why it's surprising there isn't an actual written law surrounding refs and conflicts of interest.