If ever you visit Florence in summer, try the Kraft Hotel. The rooms have pink candy-stripes, air- conditioning and cable television. On the fifth-floor terrace, you can sip Campari while enjoying silent views of the city and the olive-coloured Tuscan hills that surround it, each with a crown of cypresses and a fairy-tale white villa. When you get bored with all that, lie back and watch swifts flitting across the immaculate blue sky. Soak up an hour of blazing sunshine, then plunge into the rooftop pool.

Now that the colour of your shoulders matches that of your room, you are ready to work, to earn your brief stay in palatial luxury. Go down, get showered, change and emerge on to Via Solferino, where the heat bounces off the pavement into your face. Turn right and walk into the rippling haze at the end of the road, about a quarter of a mile away.

You will smell something burning. It is your scalp. Do not panic: economy of movement is essential in this heat. Of course, you will not find the station, even though it is right in front of you. Ask directions several times. Try the old man selling watermelon under a beech tree; the weary housewife; the half-naked mechanic.

Then ask yourself: why does being in Italy always involve getting lost/arriving too late for the football match/finding ham in the sandwich? Answer: because you do not speak Italian well enough to understand the answer, even when you ask the right question, fool. Make a mental note: must finish that BBC cassette course. If you ever start it.

Eventually, you stumble across Stazione Leopolda, once the city's railway terminus, disused since Mussolini reputedly overhauled the system. Its cool, cathedral-like darkness echoes with the sound of last-minute preparations. At one end, enormous video screens hang over the DJ's decks; along the far wall stand buffet tables decorated with fruit and flowers; at the other end, rows of bleachers face a podium.

Here, tonight, an American academic will lecture in the manner of a French semiologist on British street style for the Italian fashion industry. Your mission: to witness this post- modern Babel and report back to base.

Twice a year, Florence hosts Pitti Imagine Uomo, a huge international menswear trade show. Buyers from all over Europe and the US come to select stock for the following season; the press follows for obvious reasons. On the opening night there is always a prestigious event.

Previous seasons have seen catwalk shows by designers such as Paul Smith, Katharine Hamnett, Vivienne Westwood and Donna Karan. This time, though, the Pitti Imagine team has arranged a sneak preview of Streetstyle, an exhibition of street fashion with a heavy bias towards London, due to open at the Victoria & Albert Museum in November.

The American anthropologist Ted Polhemus has written an accompanying book, Supermarket of Style, and is here to explain how night-club fashions bubble up, eventually influencing top designers, and then trickle back down into the high street shops, thus entering the mainstream. Of course, most British kids have been drinking this in with their mothers' milk for a decade at least, but apparently the Italians still don't quite get it. So there will be an hour- long lecture with slides and relevant soundtrack.

Just to make sure there is no confusion, the Italian designer-architect Italo Lupi has constructed a vast multicoloured 'map' of street fashion, to explain the passage from teddy boys to travellers, from rockers to raggamuffins. It is 60ft long, 20ft high, with flashing neon signs indicating where each group has emerged during the past 50 years.

To complete the extravaganza, 20 assorted representatives of British youth culture have been flown in to cavort among the revellers at the post-lecture party. Backstage, you can find them putting on their Streetstyle drag, getting ready for the big show. Here is Sidone Barton, from the girly boutique Sign of The Times, slipping into fluffy white hotpants, along with matching feather boa. Over there is Dinzie Archibald, all baggy jeans and oversized sportwear, representing the raggamuffin fraternity.

Everywhere you turn, you find a ted, a goth, a mod, a superannuated glam rocker, a pixie-like creature wearing fishnet tights, tight rubber corset and tattoos on her breasts. As the evening wears on, you will notice that they are regarded as curious specimens, somewhere between alien life forms and animals at a zoo. They are filmed dancing, and broadcast live on the video screens above the DJ.

Outside, an Italian television crew is interviewing two kids with dreadlocks, and suddenly you realise why this event is such a big deal. Could they be black Italians? No chance. With dreadlocks? Impossible. The same goes for virtually every other subcult represented here.

We take our street culture for granted. Seen out of context, though, its richness and diversity is astounding. National Heritage? It is all around us, on every street corner. Our fashion is vernacular.

Italians are eagerly decoding and learning this language. Their stumbling attempts to grasp its subtler meanings may amuse us, but at least they try. And we British go on working on our tans until they catch up. Let the Yanks explain it to them.