On match days, if you stand in Jack Dun's mews garden, you can hear the crowd roar, a swell of sound filling the air with distant shouts and the shrill blast of the referee's whistle.

Dun's home is just a short walk from the Greenyards, home of Melrose Rugby Football Club and today, host of the world's most famous sevens tournament.

Dun won't be in his garden today, of course. The 86-year-old – a former player, president, referee and current club historian at Melrose – will be at the ground, cheering on the team he has supported his whole life.

More than 10,000 people are expected to pack in to the small Borders town this afternoon for the Aberdeen Asset Management Melrose Sevens. The 129-year-old one-day event, which is broadcast live by the BBC to hundreds of thousands of fans around the world, will boost the local economy by an estimated £2 million.

The host club, which won the title in 2011 for the first time in 13 years, knows the world is watching as it battles to retain the famous Ladies Cup. "We have a good chance, because we have that desire to keep the title," nods Dun. "But there are some strong contenders, like Bay of Plenty, from New Zealand. It's not going to be easy."

This year marks Jack Dun's 72nd attendance at the Sevens. "Nothing keeps me away," he smiles. "Everyone in the town gets involved, one way or another. There is a buzz, an excitement which builds up from the moment the draw is announced and we know which teams are coming."

Three weeks ago, on an unseasonably hot Sunday, that sense of excitement was already in the air. The unexpected March sunshine and high temperatures had brought a crowd of almost 700 to the Greenyards to watch an under-17s international between Scotland and England.

Families flitted between the ground and the nearby park, making the most of an early taste of summer, and cafes and restaurants hurriedly scattered chairs and tables outdoors as alfresco dining suddenly became appealing.

As war raged on the pitch (Scotland were finally defeated 15-33 in a tough match), John Reed, the current club president, was the picture of calm as he cleared a space to sit down in his tiny office at the back of the stand.

"It's getting a little bit busier for us now," he says, in something of an understatement.

Reed, who is originally from Cheshire, settled in Melrose in 1975, after graduating from Edinburgh University. The retired vet got involved in rugby when his two sons, then aged six and eight and now in their 30s, took up the sport. "They don't play so much now, but I stayed with the club, firstly in the youth team structure, then on the committee and now as president," he says. "The Sevens is as much a social as a sporting occasion. Club members host visiting players, and many people have made lasting friendships out of it."

Rugby sevens is a shorter version of the traditional game, a fast and furious contest with high point-scoring, hard hits and lung-bursting sprints played over 15 minutes – seven minutes each way with a minute break at half-time.

Teams from the world's top rugby nations regard it as an honour to be invited to the Melrose Sevens and this year, teams from across the UK will line up alongside Bay of Plenty from New Zealand, Singapore, Hong Kong Scottish and London Scottish.

The idea for a sevens tournament was first dreamed up in a Victorian butcher's shop, as a way of raising money for the cash-strapped local team. Today, die-hard fans often stop to be photographed outside the shop, located a few hundred yards up the hill from the Greenyards.

"Ned Haig, who got the credit for 'inventing' the Sevens, worked here," explains the shop's current butcher, Martin Baird. "Although, some say it was really David Sanderson, who owned the butcher's, who came up with the idea. He was a gentleman, who'd served his country. The pages of the Melrose minute book for that time are missing, apparently, so we don't really know who said what and how it all began. Ned took all the plaudits, but it's a bit of a mystery."

Baird lives behind the shop with his wife, Karen, and three children – Christina, 19, Roseanna, 17 and 14-year-old Lewis. Like most people in the town, he has a rugby connection – Lewis plays for his school team, and Baird's brother Roger played on the wing for Scotland.

"As the Sevens approach, the buzz starts to build. It swings into action a few days before, as the stands go up and people start to arrive – you recognise the same faces, and it becomes a big social occasion," he says. "The whole place comes alive. One year, we came close to cancelling because of a snowstorm in the morning, but it cleared up. We've been lucky, it's never been called off because of bad weather."

At the King's Arms, a little further down the street, owner Danny Kennedy is proud of his hotel's connection to the tournament's origins, though he's a little disgruntled by the appearance in recent years of a beer tent at the ground. "We used to be a lot busier around Sevens time than we are now – the tent takes away a lot of the trade from the businesses in the town," he says. "But we get supporters coming for a look – our bar used to be the Melrose club house, so the early meetings about the Sevens all took place here. It's good to be part of the tradition."

Tradition is important to Kath Runciman, local grandmother, Scottish Women's Rural Institute stalwart and proud Melrose supporter. The 75-year-old's three grandsons play for the club and she is often at the ground, cheering them on. "It's grand to watch them but goodness, I think they might have to start giving out blood pressure pills at the gates," she says, with a laugh. "It can be nip and tuck sometimes."

Runciman's grandson Grant plays on the back row of the Melrose first team, and has been capped for Scotland at under-20 level. His cousins Angus and Ewan are in the youth squad, and have ambitions to follow in his footsteps. Grant works on the family farm when he is not training on the rugby field, and the two schoolboys also help out when they can.

"Farming has a long tradition with rugby in the Borders," said Runciman. "Many years ago a lot of the players were sons of farmers. Working outdoors in a very physical job meant they were fit young lads. At the same time, all the farmers' wives were members of the Scottish Women's Rural Institute."

Runciman, who has been a member of Langshaw WRI since 1968, and fellow member Jean Wood, who also has three rugby-playing grandsons, have helped to revive an ancient tradition for the 2012 tournament. At the first tournament in 1883, ladies from Melrose presented players with shirts decorated with hand-sewn badges – a lucky charm, apparently, as the home side went on to win the tournament. "When we heard about that," says Runciman, "we thought it would be a bit of fun to embroider the jerseys again, and perhaps bring the boys some extra luck. Melrose has a fine team and the players train hard, but with some of the world's top teams coming to the tournament, they'll have their work cut out."

The first tournament, featured seven teams, all from the local area, but even then, fans came from far and wide to watch. Local newspaper, the Border Advertiser, noted in its edition of May 2, 1883: "By the time the event, the chief one of the day, commenced, an enormous crowd of spectators had assembled, special trains having been run from Galashiels and Hawick, and about 1600 tickets had been taken at Melrose during the day. From the former place alone there were 862 persons booked of whom 509 came by special train and the other 353 by ordinary train. The Galashiels Brass Band, in uniform, came by the special train and discoursed music at intervals, the light fantastic being tripped by a good few of the young people to its strains."

People in Melrose are proud of Sevens day, when the town becomes the epicentre of the rugby world. But one man's name comes up in every conversation about the history of the event, and the club: that of Jack Dun. Dun's love of rugby began at Merchiston school, where he was team captain in his last term (an achievement repeated by his elder son John, making them one of the few father and son pairings to hold the position in the school's history).

He watched the Melrose Sevens tournament as a youngster, and pulled on the black and yellow jersey for the first time in 1944. "But then I got appendicitis, and after that I was posted overseas with the army, to India, so I only managed a few games," he recalls. "When I came home, I wanted to get back playing for Melrose. In those days there weren't any trials or talent scouts – you just turned up at the ground for training and if you were good enough, you got picked."

Dun played at scrum half for eight seasons, during which the club won the Borders League twice and triumphed in what in 1952 was known as the "unofficial championship" (now the Scottish League Championship). When his playing days were over, he spent 17 years as a referee and joined the Melrose Sevens committee 36 years ago. "I was put in charge of the referees because of the experience I had, and I still have that role, but I'm number two, now," chuckles Dun. "There is a younger, much more able man than me at number one."

One year, Dun recalls, he helped drain the ground after heavy rain caused severe flooding. "I was out the night before, and a young chap came over to ask if he could help me," he says. "We worked on it together – it was a 16-year-old Craig Chalmers, who is now the coach at Melrose and a Scottish internationalist with 60 caps."

Dun, a retired agricultural seedsman, and his wife Jean care for their disabled son Alistair at home. They have another son, John, who runs a ski business in Val d'Isere in France, and five grandchildren, one of whom lives in Australia. The couple's daughter, Fiona, died in a car accident in France four years ago but her husband and children keep in touch regularly and often visit for the Sevens tournament.

"The world is a much smaller place now, and we are lucky that we keep in touch with our grandchildren," smiles Dun. "But I have never had any desire to leave Melrose. My roots are here – I come from an old farming family, going back 200 years here – it has always been my home."

Dun, who visits the Greenyards most mornings, is proud of the club and delighted to see talented young players making their mark in the youth squads. "The youngsters are the future of the club, and the sport in Scotland," he says. "It's good to see them getting involved, and being part of the Sevens. It's what they are aiming for."

Ross Miller, player and youth development officer at Melrose, agrees. "Some of the lads will be involved as ball boys, and there's a coaching clinic and a mini-tournament, so you can see them all getting excited as the Sevens gets closer," says the 27-year-old. "They all want to play at the Greenyards, and if you're picked for the Sevens, that's something very special."

"The town is packed around Sevens weekend – you meet some real characters. And as soon as the final whistle goes on the last game, people are booking their tickets and hotel rooms for next year. I've played rugby since primary school and I've worked for the club for seven years, so I understand the passion. I live and breathe it. It's all about the rugby." n