Fat chance. They're only at it in the middle of the square, a young couple dancing as if they're about to lose each other for ever. We've seen tango in films, but it's quite different, quite shocking, to see it in the flesh. His back is arched and his moves are dominant and erotic. Her legs trace up and down his, sudden quick flicks followed by slow, teasing ones. They court each other, reject each other and court each other again, moods swinging wildly as the music changes pace. Just to watch it feels like a cardinal sin.

In the crowd of onlookers, several older couples can't keep their feet still. Before we know it, the square becomes a dancefloor, passers-by applauding in the warm sunshine. You would never see anything like it in repressed, uptight London. It is a beautiful sight.

But there's one thing we both already admit: tango is very, very difficult. Three sun-soaked beers later, we've talked ourselves out of the evening's two-hour group lesson. We'll just watch instead. The official reason is jet lag, but really we're just being chicken.

Matt: Thank God for Norwegians. If you're ever feeling inferior in the sexiness stakes, make sure you watch Norwegians trying to dance. It's a wonderful confidence-builder. Of the four couples in the lesson, they are by far the worst. Watching them strut their stuff is the visual equivalent of fingernails down the blackboard. It's traumatic, but at the same time it is an enormous relief - we aren't that bad.

DAY TWO

Harriet: I'm dancing with Noelia's brother, Nahuel, today. To dance with an expert is a revelation, but, my, how he holds me close. My mother would be shocked - the entire length of our bodies is pressed together as we move. I have no choice but to relax into the intimate embrace of a complete stranger. There is a logic, though: dancing cheek to cheek forces me to stop looking at my feet, which has to be a good thing.

Matt: Yes, and while Harriet's getting all jiggy with Mr Flashy Pants, I have to dance with Noelia. You'd think that dancing with an Argentinian beauty would be a pleasure, but it's awful. I start by crunching her petite feet. Helpfully, my body breaks into a profuse sweat - it must be like dancing with a blancmange. By the end of the lesson, things have improved. I'm still crunching her feet, but now it's in time to the music.

Harriet: After lunch, we go shopping for tango clobber. I've been wearing comfy flat-heeled shoes up until now, so I swap them for some rude, black, glittery stilettos. Matt goes further: he buys shoes and a black waistcoat. So I go further too, and buy a dress: a long, flowing pink number, all sequined and slinky. We're like those idiot novice skiers who turn up on the mountain with all the latest gear. For tonight’s group lesson, we’ll look the part until we start moving.

Early on, we are told to swap partners. Matt goes off to frogmarch a succession of bored women around the room, repeating the same basic step over and over. I get stuck with Mr Norway, who is, although I hadn’t thought it possible, worse than Matt.

Then we change again. At last I’m being led by more experienced students: none of them can believe I’ve had only two lessons. “I can see you have been dancing before,” says a man from Taiwan. But the truth is, it’s not that hard if you have a good man.

Matt: On the odd occasion that men are roped into dance lessons, they often chuck them in early. I really wanted to break that stereotype. Which meant that I really wanted to learn the steps. But I’ve got too many things to worry about.

Tango is a chauvinist dance: the men lead, the women follow. This is proper male-dominance stuff. Great in theory, but ... I never have time to learn the steps because Harriet’s always expecting (grumpily) to be led. To lead, you need to plan the steps. Planning the steps means you can’t learn new ones. She just doesn’t understand.

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