From nine to five, Dawn Irwin is a legal secretary. Almost any other time, when the weather’s fine, she puts on her skates and heads for Kensington Gardens - the capital’s mecca for in-line skaters and Dawn’s classroom.

Dawn, who’s 30 something, is a former triathlete and a personal trainer for 13 years. She has been an in-line skating instructor for the past two, giving private lessons to an increasing number of clients. For her, wheels have become a way of life as well as a way of earning a living outside office hours.

“I have been skating since I was old enough to stand up and balance. My Dad got the whole family involved - he’s 65 and still skates every day.”

Belfast-born Dawn honed her skating skills on “quads”, old-fashioned rollerskates, during the 1970s roller disco craze. She first tried in-line at a fitness convention in Las Vegas two years ago and took to it immediately.

In-line skating was developed by two ice hockey playing brothers in the States looking for a way to train during the off season. Rollerblading is to in-line skating what Hoovers are to vacuum cleaners or Biros are to ballpoint pens - a brand name that became generic. “If I’m at a party and tell someone I’m an in-line skating instructor they say ‘Oh, rollerblading’.”

Skaters were banned from all but a few areas of the royal parks in London after a fatal accident with a cyclist in Hyde Park. “The park was getting congested, ” says Dawn. “Last summer it was way too full. It was great fun but there were no rules.” Trained volunteers from the British In-line Skating Association now patrol the parks, teaching beginners (“pavement inspectors” in skate jargon) how to stop and administering first aid to fallers.

There are rumours that in-line hockey or speed skating may feature in the next Olympics. But on its more radical fringes, in-line skating shuns the sporting establishment. So called “aggressive” skaters embrace the baggy fashions, tricks and jumps beloved of their skateboarding cousins but take them to new extremes. A favourite stunt is “grinding” - leaping on to metal bannisters or handrails and sliding down them at speed.

Dawn says irresponsible skaters are in the minority and would like to see more provision made for the sport, with the emphasis on safety and proper protective gear. She reckons the way for skaters to avoid accidents (and pedestrians) is to build more skate parks - at the moment there’s only one in London. “This is the sport of the 90s. And it’s the fastest growing recreational activity in this country - 750,000 pairs of skates have been sold so far this year alone.

“Councils should have a more enlightened attitude and build more skate parks. That way you wouldn’t get aggressive skaters spinning off kerbs and backing into pedestrians. They would spend all day every day down the skate park if there was one.”

With hockey, figure skating, speed skating - and even basketball - in-line is evolving in all kinds of directions. For Dawn, the attraction is simple. “I’m interested in the fitness angle. It’s a great way to get fit and keep fit because it’s a non impact sport and it has higher fat burning properties than running.”

Lately, in-line skating has become a favourite of advertisers. Dawn receives regular calls from people looking for film extras and has even appeared in a Twiglets commercial. By evoking a carefree Californian lifestyle in order to sell everything from tampons to cigarettes, skating’s only image problem would seem to be that it’s too trendy for its own good. But, in England at least, the reality is a bit different. “I have lost count of the number of lessons I have had to cancel because of the rain.”

Dawn is a contributor to skate mag First In Line and has also written a book based on her experiences as an instructor. The Young In Line Skater, published by Dorling Kindersley this autumn, is aimed at eight to 12-year-olds who want to learn the sport safely. It covers everything from choosing and maintaining equipment to basic moves and jumping. But the most important thing, once you get going, is to stop. “I’ve taught people from four to 74. But if you don’t know how to stop properly, you are going to hurt other people.

“When I arrived here I was the only qualified woman instructor. I did get a bit of a hard time, but I have always done male-dominated sports. When I was a triathlete I was always able to hold my own, but I haven’t been on my racing bike since I moved to England. This has taken over my life.”