His current boss -- in rugby terms at least -- is Tony Spreadbury, who worked as a paramedic in his earlier days refereeing.
'He did an early kick-off in Newport,' says Barnes retelling the tale. 'He then had to get on his paramedic kit after that and attended to a chap having a heart attack. The guy looked up struggling for breath and was a little shocked to recognize 'Spreaders' from the game, only to have to be resuscitated by him.'
For Barnes, a practicing barrister in London as well as a professional referee, the crossover is not always so dramatic but comes into full focus at times.
'Put it this way, one of my managing directors is a Welshman,' he says. 'If he feels hard done by a decision I may have made, he'll be waiting by the front door at work on Monday morning!'
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The 39-year-old is among the leading lights of referees and officiated at the opening game to this year's Six Nations between France and Wales -- from which there were no recriminations on his return to work.
As well as keeping in check 30 players, some of whom weigh in excess of 17 stone, Barnes' dual life also sees him deal with cases of bribery and corruption, mostly these days outside of the courtroom and instead in the boardroom where it is not uncommon for him to be recognized by a rugby fan in the room.
'The meeting might end and suddenly turn to the weekend's rugby,' he says. 'Someone might tell me they feel hard done by, something like 'you screwed the Scots last week,' which is all the fun of the game.'
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'Stressed people in stressed situations'
Refereeing and the law might not, on the surface, seem like they have great parallels, but Barnes believes both are a perfect fit -- from 100,000 pages of documentation in a complex case to the 250 decisions he might make in the course of a Six Nations match.
This weekend, he will act as an assistant referee for Italy's match against Ireland in Rome.
'You're dealing with quite stressed people in quite stressful situations,' he says, 'whether that be on the rugby pitch or in the courtroom or boardroom. In both, you need to take something that's quite complex and simplify it.
'And it's quite common for me to take something I've learned in my legal training into refereeing. The two switch -- sometimes rugby's the job and the law's the hobby, and vice versa. It's actually fantastic to juggle.'
In rugby, the secret to being a good referee, in his mind, is that he treats players as he would treat them off the field, with empathy and understanding.
And he believes the sign of a good game for him is that no one has noticed him.
'Take the France-Wales game, I was able to enjoy a beer with both sides after the match and no one mentioned what I'd done,' says Barnes, who avoids reading any press about himself or going on social media.
That is not to say he's not open to criticism: 'Don't worry, I've got some close mates who can keep me very grounded after a game.'
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Wave of support
Growing up, Barnes was a flanker until a knee injury at 15 forced him to give up playing, the same age he refereed his first match.
Now, he is among the world's best and, as such, will travel to the World Cup in Japan later this year to officiate. There is some conjecture it could mark the end of his refereeing career.
'People forget that referees are fans as well so the World Cup is the absolute pinnacle for me,' he added. 'After that, I'll sit down and have a chat with my family about whether I continue or not.'
His wife Polly works full-time for a marketing company while the couple have a four-year-old daughter and two-year-old son.
'It can be a juggling act but we've very supportive family,' he explains. Both children like to watch Dad on TV wherever possible. '
Their only complaint is that I don't wave back when they wave at the TV!' he adds.
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Aptly, the Barnes family home is near enough in the shadow of Twickenham Stadium, the home of current Six Nations leader England.
Rugby, he says, has enriched his life, to his eyes a respectful game that has meant for the most part he does not face the vitriol of his fellow referees in football.
He is close friends with former FIFA World Cup referee Howard Webb and received a text from Premier League referees' chief Mike Riley after the France-Wales game congratulating him on his calm approach.
'People sometimes think we stick to our own sports but we do talk to referees in other sports. You need to, it's a funny old game we do in refereeing.'
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