There's a look that passes across Jenny Frances's face as she begins to dance the Argentine tango with her husband Ricardo Oria.

As he takes hold of her petite frame, bringing her close in an embrace, the pair slot together like perfect puzzle pieces and Frances relinquishes control. She looks utterly contented yet empowered; completely in the moment, the music. Oria might be leading, but with every deliberate move he makes, Frances's body subtly and instinctively responds to the stimulus. He walks, she moves, her feet flirting with his. Their chests pressed closely together, their bodies move easily and fluidly as one as they glide like skaters on ice. Their bodies are doing the talking; and this, like every dance, is a new conversation.

"Tango is like a language," explains Frances as we sit down for a coffee in the couple's studio in Edinburgh's Leith Walk. The walls are covered in posters and flyers advertising their many workshops, milongas - social dances where people tango - and performances from around the globe. "It's got lots of rules. You spend a lot of time learning them, but then you can say what you want," she smiles.

Frances, 35, and her Argentine husband, 34, have been dancing together since they fell in love, and teaching tango for almost as long, since 2002. When the pair came on to the scene in the early noughties - Oria first, straight out of Buenos Aires, the birthplace of tango - the Scottish tango scene was very small, but enthusiastic, he recalls. Over the past decade that has mushroomed as more people across Scotland - of all backgrounds, professions and ages, from 18 to 80 - have embraced tango; become addicted, even. It's that kind of dance, it seems, and those who do it are passionate about its joys.

There are milongas and tango classes happening weekly in cities and towns across Scotland, including Aberdeen, Glasgow and Edinburgh, as well as annual gala balls in the last two cities. Frances and Oria have arguably been at the heart of the dance's popularity here, and while they insist they can't take all the credit, their classes in Edinburgh, weekend workshops and sessions in Aberdeen and Glasgow - where they have proteges teaching on their behalf - have undoubtedly encouraged the trend.

People start tango for a variety of reasons, they say. There are those who simply want to dance, while others want to meet people. Some have seen the tango on Strictly Come Dancing (though the Argentine tango, danced properly, is nothing like the version you see on TV) and are drawn to the romance of the dance or because they like the music.

Those who continue, says Frances, are searching for a feeling of connection with another person. "It's that conversational aspect. Tango is very intimate in its embrace and involves a lot of improvisation - it's magical. It can be simple or complex and there's a lot of nuance."

Oria agrees. Because it's an improvised dance, he says, you're creating on the go. "That's cool. You will never dance the same tango."

There's something else, states Frances, and that's the embrace. "There's no hip grinding, wiggling or anything overt," she says, "but at the same time, you're really close. There's a lovely intimacy to it and after three minutes you let go."

There are people coming to Scotland to dance tango, Oria tells me. The four-day Edinburgh International Tango Festival, run by the Edinburgh Tango Society, takes place each May, attracting tutors and dancers from around the world. Likewise, tango enthusiasts from Scotland frequently travel to tango festivals around the globe.

It's the mystery that appeals, reckons Oria. It's also a dance people can do alone; anyone can attend a milonga, you don't need to have a partner. "You wouldn't believe how into it people get," says Frances. "People who tango are known for being very serious about it."

Frances and Oria are, predictably, "fanatics" about the dance. I, on the other hand, am a complete novice. We discuss how it is possible to live your life without knowing what tango is, despite these milongas and classes happening around Scotland. "It's an underground world. It's an underground world in Buenos Aires as well," says Frances. "People are more aware that tango exists, but a lot of our friends in Buenos Aires don't dance tango and would be mortified if we made them. They wouldn't know which foot to put where." Like me.

Oria invites me to dance. He compares the tango in Buenos Aires to Scottish dancing here; we all know of specific dances but we don't all know how to do them. "Stretch your leg back," instructs Frances. "Lean your chest into him. He can take it."

It feels quite strange and it quickly becomes apparent that I'm not a natural. Tango is not easy. "We have a saying that tango is for the brain, because it does have a bit of a learner's curve," says Frances.

This, strangely, is perhaps one reason people get so hooked, because they have to commit so fully. It brings out the best and worst of people, Oria tells me. If, for example, you are impatient, learning tango will exacerbate that. The brave people who continue have worked through the worst aspects of their personalities, a process, he says, that is amazing to watch. And because it's such an intense dance, it seems you must express how you're feeling at the time in order to truly dance well.

Oria was drawn to tango at age 13, in an attempt to win a girl. "Nothing happened," he laughs, "but I stayed doing tango." He wasn't good immediately - his friends called him Robocop because he was so stiff - nor did he love it. "You have to go through a period of love and hate. But once you get through that, it's amazing."

He changed teachers, improved and, by his late teens, was dancing professionally. At 21, he quit studying psychology and accepted an offer to teach tango in Edinburgh, where he met Frances, who was working at the Scottish Executive. She was already obsessed with tango having seen a film called Tango, by Carlos Saura, while at university. She found a flier in the programme from the Edinburgh Tango Society. "They were trying to get more people to go along, so I went. That was it. I loved it."

After she met Oria, she realised tango was what she wanted to do for a living. "People who do tango professionally start as a hobby - it's not on your [list of] career choices. It just becomes more important to you and then at some point you have to make a big leap and say, 'I want to do this.'" The couple decided Frances would join Oria in teaching and since then, tango has been their life, in philosophy and practice.

"If we are having a fight at home," says Oria, "We dance the tango and that's it, fight sorted."

Phillip Fisher, 69, is a retired Puma helicopter pilot who lives in Aberdeen and has been dancing tango for 10 years, both in Scotland and in cities as far apart as Vancouver, Berlin and Singapore. He marvels at the international addiction to tango and its ability to break down barriers, allowing people to converse in a way that could hardly be achieved if they were speaking the same language.

To Fisher's mind, Frances and Oria are the best tango teachers he's met and he frequently attends their workshops. He is also one of the volunteers behind his local tango group, Tango Aberdeen. While the group has a mix of ages, their numbers fluctuate, he says, due to the transient nature of people living in the city for university or the oil business, so they are always keen to attract more people.

"When you get that connection with somebody - and it happens only now and then - it's magic. I can't enthuse too much about it. It sounds a bit loony," he laughs. "If you can immerse yourself in the music and both get that same level of absorption, that's when the magic happens. Anyone dancing tango wants to achieve that."

Recently, while attending an afternoon dance called a tango tea, he found it. Having hit it off with a random partner, the pair spent the whole afternoon dancing together. When the dance finished, they parted ways. "It's a sort of innocent indulgence," explains Fisher, who says he wants to keep dancing as long as he can stand.

While you can dance with one partner in tango, the custom is to dance with lots of people, usually for the duration of a tanda, a set of songs, usually three or four, between which a cortina is played to allow people to change partners. Traditionally, you follow the cabeco, where a gentleman nods his head to a woman as a signal to dance and the woman returns his gaze as acceptance so as not to cause any offence if she doesn't want to dance. In the UK though, this is not common practice; people will simply ask you to dance.

The tango is a very different experience for men and women. The man, as leader, drives round the dancefloor, thinking of the next move, whereas the woman is being guided by him, "speaking" back with each move. Many women even close their eyes for the duration of the dance.

I notice this when I attend a Sunday afternoon tango tea in the St Andrews East Church in Dennistoun, Glasgow. It's dreadfully dreary outside but here the atmosphere is like a brightly lit wedding, with people of all ages, even children, gathered at tables, chatting and eating. Couples move around the floor, tango dancing. A band is playing traditional tango music (the music in tango stretches from the 1920s to today) and there is a table covered with cakes. Next to it sits a woman in a fluorescent pink skirt, waving a fan; some men wear jazzily patterned floral shirts and the women's shoes are really quite something. A lovely older couple seem glued to each other, oblivious to everyone around them. It has a very different feel to the darker, more intimate, atmosphere of the evening milongas, where people can be more dressed up. Today, people are welcome to be as casual as they choose.

I'm here with Alistair MacDonald and Shona Barr, who run the event and teach tango in Glasgow. The pair also organise events which attract dancers from across Scotland and the north of England.

Having met at Oria and Frances's lessons, the two eventually began teaching classes in the city and continue to be trained by them. Macdonald, 51, is a lecturer in composition at the Royal Conservatoire of Scotland by day, while Barr is an artist and, unlike Oria and Frances, they are both married to other people. Barr, in fact, met her husband at tango lessons.

She says, "The tango scene has gone from this little niche thing where we all knew each other and met at the Tango Bar on a Wednesday night [in Glasgow's Blackfriars bar] - because that was the only thing on - to now, with so much on."

Barr loves the pace of tango which, unlike full-on salsa, can be slower; Macdonald cites the musicality and playfulness of the dance. "I find improvising with the music fascinating," he explains. "You never stop learning tango. The better you know the principles, the more you can improvise, although you don't need to do anything fancy to be a really good dancer. You could do the simplest thing and have the most amazing dance."

Like MacDonald, Yorkshire-raised Rosie Staniforth feels an affinity for tango's soundtrack and says you have to dance like you're in love - with the music, not the person. An oboe player with the Scottish Chamber Orchestra, she has been dancing for seven years. She was looking for a hobby, but says her obsession with tango didn't kick in until she took a sabbatical in Buenos Aires in 2011, where she's now got friends and to where she returns to dance - sometimes for eight hours a day - twice a year. She seeks out global tango spots when on tour - Vienna, Brussels, Luxembourg, to name a few - and says her next stop is the Far East. She finds the Edinburgh tango scene to be one of the best outside of London and loves dancing at milongas in the Maryhill Burgh Halls in Glasgow where Hunter Reid, the project coordinator for the hall's trust and avid tango dancer, had special flooring laid so dancers glide across it like they're at the Tower Ballroom in Blackpool.

She says one of the great things about the scene is that it is so social; you dance with whoever asks. There's a mixture of singles and couples but people are not there to pick others up, like in a club, she says. Although she admits that you do get the odd tango romance blossoming.

Staniforth also cites "the embrace" as a reason's for people's fixation. "People go on about oxytocin, that chemical that is released [in the brain] when you are in a tango embrace" - the same hormone that's released when you hug or kiss a loved one. "I don't know if there's any truth in that, but I certainly find it comforting, and you see people looking like they're in a trance a lot of the time."

That said, there's no predicting what kind of connection you'll have with somebody, she says. Two good dancers could have no chemistry, for example. "It's a weird, magical thing. You can't pinpoint why something feels brilliant or why something is not working. But it absolutely keeps it interesting.

"People don't seem to be bothered what your outside situation is either. We are all united by our love of and slight addiction to this beautiful dance. You can tell that's why people are there." n