Two madmen on two wheels

The evidence of spittle was still prominent on my shirt three hours later: a map of New Zealand spreading indelicately across my shoulder, fading to a shade of armpit yellow. It was something the pedal proselytisers had neglected to mention. All last week they were out and about, telling us of the beneficial effects of cycling to work,how it would expand your cardiovascular capacity, increase your life expectancy, end pollution at a stroke. Yet none of them remembered the all-important advice to invest in specialist stain remover.

There I was in the middle of National Cycling Week, head down on my way to the office, when I became victim of a new form of urban condition about which the biking lobby keeps wisely silent: cycle psychosis.This is the pedal equivalent of road rage, a sudden overwhelming anger which turns the gentlest of riders into a boiling madman. Under its influence victims will grab anything to hand, cycle clips even, to use as offensive weapons in their desperation to inflict maximum injury on those who cross them.

I've noticed increasing evidence of the affliction as I've cycled around town: last month, it was a gent in the City perching on the saddle of his Moulton as he tried to smack a bus driver through the door of a Routemaster; last week, I watched a mountain biker in Holborn whimperingly clutching his knuckles after he had rabbit-punched the boot of a taxi; every time I go there, cycle messengers along Oxford Street are goggle-eyed with fury as they plunge into flocks of tourists attempting to cross on a red light.

And you can only sympathise. You can understand why we cyclists, vulnerable up there on our saddles, feel threatened by road-users with an apparent blind spot for anything with fewer than four wheels sharing their tarmac. Which is why I had taken to cycling to work along a canal towpath: along there, I thought, I would be safe.

And for six months this has been the case. It is not only a life-preserving experience pedalling gently along the banks of the Grand Union, it is life-enhancing. At this time of year, you see things you do not expect to see in the middle of Islington, Hackney and Poplar - things which fill the leaner, fitter heart with pleasure: a heron on patrol for frogs, a swan carrying its freshly hatched cygnet on its back, four shouty youths attempting to cross the canal on a large piece of polystyrene and sinking.

There are, of course, problems you don't encounter along the Commercial Road: fishermen unable to control rods the size of telegraph poles; a large rat consuming the entrails of pigeon right in front of your path; or the friends of the four shouty youths who, when they see you sniggering at their mates' watery distress, start throwing stones from the opposite towpath.

But at least, along there, you don't come across barking road-users. Especially since an informal etiquette has developed among the cyclists. Everyone has bells on their handlebars to sound as they negotiate the blind bends underneath bridges and to tinkle gently to warn pedestrians of their approach. Take cars out of the equation and there is no madness; there is no psychosis where the bike is king.

Thus it came as a shock when, yesterday, I was cycling near the place where the Canada geese hiss if you get too close to their goslings, when I was passed by a rider tearing in the opposite direction. I don't know what I did to upset him, but as he swished by, he yelled: "You arsehole!" and unleashed a thick shower of phlegm at my head.

Suddenly, I was overwhelmed with cycle psychosis. So incensed was I by the injustice of his assault that I turned my bike round and gave chase. I had snapped, and as I strained to catch up with him, I worked out how to make him pay for his rudeness: death would be lingering, and it would be painful. Fortunately - since undoubtedly, had I caught him up, it would have been me rather than him with a chain wrapped around the helmet and a bike hurled into the water - he sped into the distance, wishing me, as he disappeared, good fortune (at least I assume that was what the gestures over his shoulder indicated).

When I gave up the chase I discovered the other main characteristic of cycle psychosis: it abates as rapidly as it seizes. As I sat slumped across my saddle, apologising breathlessly to the man with the child on his crossbar who had been forced into the bankside nettles by our comedy chase, I looked at my shirt. The hideous smear across it had been caused, I realised with mounting shame, not by my assailant, but by me, deep in the grip of cycle psychosis, foaming at the mouth.

Tomorrow, I think I'll go by bus.

Miles Kington is on holiday.