Marius van der Westhuizen has refereed an England training game ahead of taking the role of assistant referee in Saturday's clash with Ireland, according to The Times.
The South African was invited to Pennyhill Park by England head coach Eddie Jones, who is preparing his side to try and deny Ireland a Six Nations Grand Slam at Twickenham this weekend.
While it is not uncommon for referees to assist teams ahead of international matches, World Rugby's rules stipulate that a referee is not allowed to work with a team they will referee in any given international window.
Jones' actions do not contravene World Rugby rules as the stipulation does not extend to assistant referees. Van der Westhuizen will take a flag rather than a whistle on Saturday, with Australia's Angus Gardner relieving Jaco Peyper of refereeing duties.
England will be hopeful of drastically improving on the ill-discipline they showed during last weekend's 22-16 defeat to France, where Jones' men conceded 15 penalties on their way to consecutive defeats that leave them in danger of a fifth-placed finish ahead of the final round of fixtures.