England have denied a conflict of interest after one of the officials for their Six Nations clash with Ireland refereed a squad training session Tuesday.
Marius van der Westhuizen will run one of the touchlines at Twickenham Saturday with Angus Gardner taking charge of a match that could yield a Grand Slam for Joe Schmidt's newly-crowned champions.
World Rugby permits referees to assist players and coaches with their understanding of the laws and their interpretation, and as a result an official oversees live training at England's Surrey training base on a weekly basis.
It is forbidden for an official to help a team if they are to referee them during the tournament, but as Van der Westhuizen will act as an assistant referee only, no rule has been broken.
Asked if using the South African was appropriate given his presence at Twickenham, defence coach Paul Gustard said: "Why wouldn't it be?
"So they [Ireland] will be questioning his integrity? You could see it the other way, couldn't you? What if it goes against us. He's an international referee. He is one of the best referees. You're asking someone to come in here and assist in training, give his viewpoint on things.
"It's no different to if someone from Ireland rang up to give his viewpoint on things. They have the same access. I see no issue with it at all.
"This had been long in the pipeline. It is all part of understanding different referees, how they referee things. We have a relationship with the English referees that assist us.
"The opportunity to get other foreign referees in to give their viewpoint in how they see things is important for our growth as a squad."
At Twickenham England will attempt to outwit the mastermind who oversaw their own defence for four years and is now performing the same role with success for Ireland.
Andy Farrell worked under Stuart Lancaster, whose expertise has revived Leinster's fortunes, before the pair headed across the Irish Sea in the wake of the failed 2015 World Cup campaign.
James Haskell is set to be restored to the back row in place of the injured Courtney Lawes and the Wasps flanker insists England have "intimate knowledge" of the way Farrell operates, most recently during the British & Irish Lions tour to New Zealand.
"Andy is a world-class coach. He speaks very well, he's a great orator and he obviously motivates," Haskell said. "He always demands passion and intensity from his defence with aggressive line speed and that physicality he instils into the guys.
"From my experience from working with him he always gets his boys on the edge. He demands big acceleration and physical contact. We have intimate knowledge of that."