Cycling? But I'm far too young to die

Eye witness: National Bike Week. A reluctant and frightened biker has a surprise conversion on the road to Soho Square

Why not cycle to work? People who ask that question are usually whippet-thin and pedal 40 miles before breakfast. But this is National Bike Week and the organisers want all us flabby slobs to get off our fat arses and climb back into the saddle. "It will do you good," they say. So why not? Here's my answer: it's too far; there are hills; I've got a bad back; I stubbed my toe yesterday; it might rain and I feel a bit fluey. Oh, and I don't want to die.

My friend Simon, a passionate pedaller, had a nasty accident last year and was nearly knocked off again a few days ago. I'm scared, I tell him. "On your bike," he says. "Work up a sweat. It will do you good."

The National Cycling Strategy website thinks so. "Cycling offers a low-cost commuting option, and for many people in urban areas it can actually be quicker than a car. Congestion isn't a problem for the cyclist!" Notice that over-eager exclamation mark? These are the sorts of people who would plunge into the North Sea and order their sobbing, shivering children to follow. What about congestion of the nose, mouth and eyes as you wait behind a bus, swallowing the output of its belching exhaust pipe?

Men who ride are twice as likely to have difficulty getting an erection as those who don't, according to a study published by University Hospital, Brussels, today.

Still, the NCS insists that regular cycling is good for your health. Everybody knows people in Britain are getting fatter and need to do more exercise. There is also evidence of reduced depression among cyclists, apparently. So here I am at Edwardes cycle shop on Camberwell Road.

"This is a Giant Regent's Park with an aluminium frame, gel-filled saddle and semi-slicks," says Gary, the boss. I haven't a clue what he's on about but it looks nice. "Good bike. Costs £325. You could lose some of that weight, riding one of these. It will do you good."

I do wish people would stop saying that. Now I am wobbling slowly along a back street with Steve Wagland, an instructor from a company called Cycle Training. "It makes all the difference to your confidence and therefore safety to get a bit of tuition," he says, "but the majority of adults who come to us are women. The men are too macho. They just want to get out on the road risking life and limb."

Instinct and childhood experience tell me to keep to the edge of the road out of the way - but that makes the cyclist semi-invisible and unpredictable to drivers, says Steve. Riding on the pavement is forbidden, as is going through red lights. "It is not you versus the traffic - you are part of the traffic. Behave like it and drivers will keep a safe distance. The further out you go the safer you will be."

The theory sounds good, until we place ourselves beside tons of speeding metal on Walworth Road. "Take the lane," shouts Steve above the din, gliding out into the middle of the road. There are cars coming. It feels lunatic, suicidal, but I follow. We do not die. "You see? They respect you if you are confident and your signals are clear."

Flapping about like a seagull with an injured wing is dangerous when you are pedalling like fury to stay ahead of the Number 12. Buses loom up behind us, brakes hissing as they block out the sun. But I learn that bus lanes are a sanctuary, allowing cyclists to travel in relative calm and safety while the cars snarl alongside.

"Roundabouts are the most daunting feature of riding in the city," says Steve as we approach Elephant and Castle, the most daunting roundabout in London. I would hesitate to go round it in a car. "You lead," he says. I want to lead to the pavement, the Tube station, or, better yet, the pub. But no. Weight on the pedal, push down, cycle hard across the stream of traffic and "take the lane". It is frightening but exhilarating, and feels strangely safe.

"Never mind the honking," says Steve. "Don't think of a horn as the driver having a go at you. It just means they can see you."

By Waterloo Bridge I am enjoying myself. We are moving much faster than those suckers in their cars, and the sudden rush of clean air as we cross the river is energising. Then the buildings close in as we descend into Covent Garden, and freewheeling past the cafés loses some of its glamour when you are hacking and coughing from the fumes. "Sometimes you wipe your face with a cloth after a ride and it is black," says Steve. "But the studies show that the pollution levels are actually worse inside a car."

Not that he owns one. Steve is a diehard of the kind whohave successfully campaigned for cycle lanes all over the country. They will be holding bike clinics, family cycling picnics and other events all week, including a mass ride in Bristol this morning and a dawn procession up Primrose Hill to mark the solstice on Saturday. And they will be trying to encourage people to cycle to work.

Gulping down water in Soho Square, stressed, filthy and exhausted but glowing with sweat and a sense of achievement at our six-mile ride through the city, I can almost see the appeal. Have a go. Much as I hate to say this, it might do you good.