It's sheer laziness that makes me do it. Every morning, the choice is between getting up now and going to work by public transport, or staying in bed and going by bike - which is no choice at all. Once, for a short period, I had a job to which I could commute as quickly by train as by bike. Sheer laziness made me take the train.

But cycling from Camberwell into town - to anywhere in an arc stretching from Chelsea across to Islington - is a journey of only about half an hour, door-to-door. The prospect of going out of town, up the long hill to Crystal Palace, all the way back across London and up the hill to Kenwood, then down again into the City, was more daunting. Two hours altogether? Probably. Going by car would be more pleasant (laziness again) and, I guessed, quicker.

Only three minutes down the hill from Crystal Palace I was already ahead of the car, at least financially. The little toll gate on the Dulwich estate, the sort of anachronism worth 70 points in the old I-Spy books, charges 50p for cars but lets bicycles through free. I had other advantages, too: it was a beautiful morning, and even before Dulwich village there was the treat, more highly valued by the cycling commuter than sunshine, of a traffic jam. I scooted along the gutter past a line of cars, and joined the other cyclists right up at the front, just beyond the traffic lights. An I-Spy book for cyclists would rank as high-scoring rarities things such as a courteous taxi-driver giving way to a cyclist, or a signposted cycle route which offered direct access to anywhere useful. The sight of a fellow cyclist actually stopping at a red light would warrant a few points, but the really commonplace - potholes big enough to smash your front wheel, BMWs ducking and diving to win a car's length, motorbikes blocking the gaps you could get through - would be worthless. At least on the familiar home-to-work section, from Camberwell to the south face of Waterloo Bridge, dead-flat and almost dead-straight, I knew where the hazards lay. And the pleasures: good, solid traffic, the cars moving slowly enough to render them harmless, and the wide-open bus lanes spoiled only by the buses.

Most of central London is delightfully flat: the only 'hills' are the bridges across the Thames. The long slog up on to Waterloo Bridge is hard enough to give the mountain-bike boys, irritatingly sprightly on the flat, their come-uppance from riders on lighter racing bikes. But my relief on reaching the middle of the bridge was tempered by the fact that all I had done was the easy bit. North of the river, the traffic should be lighter, making the car faster; and there was the long climb from Chalk Farm up to Hampstead Heath to slow me down. Not much happens on a bike ride. You don't meet people, reading is out of the question, you can't listen to the radio. (True, some riders use a Walkman; I prefer to listen to the threat I can't see, the traffic behind, rather than put loudspeakers in my ears.) The lone biker develops a guerilla mentality, fighting cars, hills, and painful thighs, and often dresses for the part with a crash helmet, shades, and a mask. I started wearing a helmet when a girlfriend pointed out, unkindly, that at my age my head was the only really valuable part of my body. But the dangers of commuting by bike are exaggerated: statistically, riders under 11 years old are most at risk of injury, so I passed the dangerous age 33 years ago.

Competitive spirit helped me up the last climb. Usually, you can never find a traffic jam when you want one; but Hampstead was congested enough to give me a chance of victory over the car. I rode like the wind across the Heath, and skidded to halt on the gravel of Kenwood House 49 minutes and 20 seconds after leaving Crystal Palace, more than 14 miles away.

Eventually, the car driver turned up, too.

The great virtue of cycling is that, punctures permitting, it is so predictable. The following day, even with bomb scares, road works and signal failures, the same journey would have taken 49 minutes and 20 seconds. Well, maybe 50 minutes.

(Photograph omitted)