I would have to research it, Newby. As far as I know, every Premiership game - not just the ones on BT Sport - will have a team of four - Ref and two assistants + TMO in a van. Unlike soccer, this seems to work very well, with play continuing while potential offences are checked, sometimes at the instigation of the ref, sometimes the TMO. I'm not sure if there's a citing officer present at every game; nor do I know whether Team A can instigate an investigation of an act by a Team B player. The regulations will not be the same for International matches as for domestic ones.
I have read minutes of disciplinary hearings, and the system is quite impressive. An offence will carry a tariff of, say 4 to 8 weeks, if a guilty verdict is reached. [In the amateur days, when the referee was 'sole judge of fact', a player could not be found 'not guilty' except in the case of mistaken identity. They used to hand down a sentence known as SOS in doubtful cases - sending off sufficient. When the game became professional, this system was no longer legally safe.]
Anyway, nowadays they will decide whether the offence is lower end or top end of the range. Everything is taken into account. Referee's report, player's response, video footage, player's previous record and degree of contrition, both on the pitch and at the hearing. With all this, they can reduce the sentence by up to 50%. Not sure if they can increase it. So, the wrong-footed player who high-tackles an opponent, then immediately shows remorse and concern for his victim, will get away with 50% of 4 weeks, or whatever the tariff is.
Where there has been a change - one that concerns me - is that the referee no longer is able to consider 'the apparent intentions' of the tackler. You used to be able to say: no intent, therefore no foul play. Nowadays, contact with the head is foul play. If the player ducks into the tackle, or the tackling player is jostled in the act, or if the arm bounces up off the ball, for example, that counts as 'mitigation'. It must be a penalty, because it's foul play, but the referee and his team have the option to choose red, or yellow, or just a penalty.
It seems to me that the referee is no longer trusted to make the gut-feeling decision that sympathetic refs used to do. There was an Australian sent off in this summer's series against England. He had had his hair pulled I think, and retaliated with a token head-butt, for which he was both sent off and suspended. My gut-feeling decision would have been to yellow card the hair puller (if seen, I'm not sure he was) and tell the Aussie not to be stupid, and get on with the game. I wouldn't even have reversed the penalty, so minor was the head contact.
Suspensions in RU seem to be much longer. My current bugbear is the 'deliberate knock-on' offence. I really do think a lot of them are not deliberate, and some of them are not even knock-ons! But yellow card and penalty-try is often the outcome. [It does actually come under the foul play regulations, for reasons too complicated to explain.] We would have won the World Cup in 1991, and Campese would have been sin-binned, with present-day rulings.