(CNN) Dave McNeilly remembers the days when caddies bunked in four to a room at tournaments, earning just enough for beer money.

In those days, many bag men turned up at tournaments stinking of booze.

The job, and hence the professional approach, has changed immeasurably with the money at stake.

At this week's British Open , the winner will walk away with a cheque just shy of $2 million and, with most leading caddies earning about 10%, it is a potentially gargantuan payday.

McNeilly, at 66, is one of the oldest in the field and is confident his player Matt Wallace, who was tied third at the PGA Championship and tied 12th at the US Open , can clinch the ultimate prize. But he credits Tiger Woods almost entirely for the paydays on offer.

"Tiger's arrival changed the game, for caddies as well," McNeilly told CNN Sport.

"In the past, back in the 80s, caddies would arrive smelling of drink, you don't see caddies arriving drunk now.

"Caddies go to the gym instead of the bar. Me, I go for a drink of water in the gym. But we're so much more professional now, there's great incentives and a lot of money to be made."

Caddie David McNeilly with player Matt Wallace at the 2019 PGA Championship at Bethpage.

McNeilly has been around long enough to see a stratospheric change in his profession, caddying for the likes of former world No.1s Nick Price and Nick Faldo as well as Europe's next Ryder Cup captain Padraig Harrington before his most recent pairing with Wallace.

For him, it was the Faldo connection that really sparked his career progression -- and one which he nearly screwed up on their first encounter.

"I was put in touch with him as he needed a caddie and, at the end of the conversation, he asked if I had a wheel [a device back then to measure the golf course]," said McNeilly.

"I said, 'I don't have a car, I use public transport.' The phone went quiet for a good 15 seconds as he lay down on the floor laughing silently. Then he said, 'OK, David, bring your double-decker bus' and thankfully and amazingly it all worked out well in the end."

A sense of humor is crucial in the caddie profession, according to McNeilly. So too, a rhino-like skin as driven sportsmen and women often take it out on those nearest to them.

"The stuff that Nick said to me on the golf course was hard to take," recalled McNeilly.

"But I was so thick skinned and so desperate to learn, I didn't know any different and he'd apologize after the round -- 'Sorry, I was a bit hard on you.' I was OK with it but, if a person is a p**** off the golf course, then you think twice. It's important to have self respect."

Terry Mundy boasts one of the longest player-caddie partnerships in the game, having worked for 13 years with Englishmen Ian Poulter, who has won 17 times around the world and has finished in the top three at majors on three occasions.

Mundy only got into working as a caddie when asked to stand in for a sick friend at his local pub. He became a bagman full-time when given voluntary redundancy from his job in the printing industry. At the time, he planned to do it for six months to a year and then find what he called "a proper job".

So what does the job entail? "It's hard to define but a caddie is a little bit of everything really," he said.

"First, it's our job to understand the golf course, it's a bit like the navigator to a rally driver. You're there as a support system, knowing the wind, how a shot is playing, where you need to land it and what it's going to do.

"But there's the psychology side. The conversations when a player's five over or five under are very different but you need to get the best out of any situation, to turn a 76 into a 74 or a 66 into a 64. You need to know when you need to speak up and, more importantly, you have to know when to shut up."

Tiger Woods celebrates with caddie Joe LaCava after winning the 2019 Masters at Augusta.

At 52, Mundy still loves the job -- "apart from being a sports person, it's the next best thing" -- although his body has felt its impact with three herniated discs in his back causing him to take time away in recent years.

He has known caddies who have not liked their employers, but still click on the course. But his friendship with Poulter has been the secret to their success, he says.

"Like everyone else, I think I thought he'd be brash, cocky and arrogant," said Mundy, looking back at their first pairing.

"I had the same perception as everyone else but that's just his on-course persona. We have the odd giggle and he's a great family man. I knew within half an hour of working with him that we'd be good. I think of him as a great mate and our friendship has helped the longevity."

When he began, Mundy was scrabbling to break even as a caddie, sharing a room with three others at tournaments to keep down costs. There are still times when caddies feel treated like second-class citizen, he says.

"You still get some things that happen and you think, 'You cannot be serious,' when you can't get food or a place to even stand inside when the weather's dire and play's been abandoned," he said. "But we're looked after better and better each year."

Mundy (left) wearing Augusta's traditional jumpsuit while working for Ian Poulter at the Masters.

Mundy and McNeilly have earned an impressive living from their craft, but caddies are often at the whim of their employers. Some golfers are often quick to blame their bag men and part ways with a caddie.

"It's never a nice feeling if you get the sense you're going to lose your job," said McNeilly.

"It's a fickle game and I've been fortunate. I've been lucky with the players I've worked with. I work hard and I like the players I work for to work hard, too. And I'm always learning in a non-stop business. Once you think you know it all you're in trouble. My job is still to get the best out of my player."

While most people of his age are in retirement, the Northern Irishman has no plans to hang up his caddie bib. The one thing missing from his resume is a major win, and he believes he can achieve that with Wallace before retiring.

"The reason I caddie is to have fun," said McNeilly. "But it's also to contend in the majors."

As for Mundy, he thought an elusive major might finally come his way in the latter stages of the Masters in April, only for Poulter's challenge to falter late on as Woods came through to clinch his 15th major title.

Both remain reliant on their employers to shine in order to earn a living, but with both players earning in excess of $1 million already on the PGA Tour alone this season, neither McNeilly or Mundy are likely to have to resort to the room shares of their early years.