The England captain, Owen Farrell, has had to change his tackling technique amid fears of a flurry of red and yellow cards at the World Cup. Farrell was involved in two high-profile incidents where no-arms tackles went unpunished last autumn but directives from World Rugby issued at the end of last season state he should have been punished.

Eddie Jones has already warned how the World Cup could be “destroyed” by inconsistent refereeing of the tackle area but England’s defence coach, John Mitchell, revealed on Sunday that Farrell has taken measures in training to alter his approach, with the squad on high alert over red and yellow cards.

When World Rugby issued its directives Farrell’s shoulder charge on South Africa’s Andre Esterhuizen was used as an example in an accompanying video to demonstrate when a yellow card should be awarded. Farrell was not sanctioned during the match by the referee, Angus Gardner, denying South Africa the chance to kick a penalty at goal with the clock red and condemning them to a 12-11 defeat. Three weeks later Farrell’s no‑arms tackle on Izack Rodda also went unpunished in England’s victory against Australia with the Wallabies furious they were not awarded a penalty try.

At the time England played down concerns overs Farrell’s technique but in light of World Rugby’s edict, which led to four red and 13 yellow cards at the Junior World Cup this summer, Farrell has been working specifically with England’s strength and conditioning coach, John Carrington, who also acts as Mitchell’s assistant in defence. “[Owen’s] not overly focused in that area but he has made some adjustments,” said Mitchell, who has attended a meeting with World Rugby’s head of referees, Alain Rolland, to discuss high tackles.

“John Carrington is very good at the tackle technique, so they’ve just made some adjustments based on that. If your hand is in front of your shoulder then you’ve got a better chance of making a proper wrap tackle. If your shoulder is ahead of your hands then the law probably doesn’t look after you very well. At the back of everyone’s mind there were a lot of cards issued at the U20s world tournament. There will definitely be some apprehension around, ‘OK, is it actually going to be like that?’”

Last month New Zealand’s Scott Barrett was sent off for a shoulder charge in the All Blacks’ heavy defeat by the Wallabies and in their final match before the World Cup they chose to play the last 15 minutes of their 92-7 victory against Tonga with only 14 men, removing Ryan Crotty in an effort to practise with a numerical disadvantage. Mitchell revealed that England had planned to do likewise in their record win over Ireland last month and, while circumstances dictated they opted against it, they frequently do so in training.

“We constantly underload and overload [numbers] in training, to be able to adapt to these situations,” Mitchell said. “To be able to cope with the worst-case scenario is really important. We have trained two down [13 men]. It’s a very complex area as it is, so it is our responsibility as coaches to make it absolutely clear to the players what they can and can’t do. Calmness and clear heads create the ability to make good decisions and collectively you end up working together, and it comes through the way we train.”

England begin their World Cup campaign against Tonga on Sunday amid doubts over the fitness of Joe Cokanasiga and Mark Wilson, who both have knee problems. Tonga have a somewhat stereotyped reputation for being overly aggressive and Mitchell has warned that sides who do not focus on reducing the tackle height will come unstuck.