If Isaac Newton was alive was today, it wouldn't take an apple to land on his head to teach him about the force of gravity. He'd take a trip on the London Underground instead. As every GCSE science student knows, the force of gravity increases the nearer you get to the earth's core. One consequence of this simple rule on daily life in the capital is that the deeper you go into the Underground system, the more slowly people move. The effect becomes so intense that in the really deep tube stations, such as on the Piccadilly line platforms at Holborn, hardly anyone moves at all.

But gravity in London also has a differential effect, according to where you come from. Like long-distance runners brought up on the high-altitude/low oxygen slopes of Kilimanjaro, long-term London residents become acclimatised to their environment. So while they sweep swiftly down the tiled corridors beneath their city, hastening to make their connections on the Misery Line of their choice, tourists and visitors drag their sluggish legs around each corner as though the floors were paved with treacle. Disorientated and confused, they halt at regular intervals trying to make sense of their surroundings, studying maps, performing unpredictable U-turns like black cab drivers let loose on foot, and generally getting in the way of people who've been in training for these journeys all their lives.

Don't let anyone fool you with that old cliche about it being "better to travel than to arrive" in London. It isn't. Better by far, if you've got the choice, to live over the shop and let others come to you. Rest assured, the time is coming when, like the Victorian industrialists of old, the forward-thinking employers of tomorrow will be providing their workers with places to live within walking distance of work.

At the turn of the last century, futurologists were warning that if the volume of horse-drawn traffic continued to increase at its current rate, London would disappear under a mountain of horse manure within a matter of a decade or two. Trams, buses and the gravity-stuffed London Underground spared us from the worst of that particular peril. Instead, today we have the internal combustion engine and a quarter of the land surface of central London given over to the motor car. We have air quality that is worse (due to invisible pollutants) than during the era of the great London smogs before the Clean Air Acts. And we have an average traffic speed -- somewhere around 10-12 miles per hour -- that is about the same as in the days of horses.

There are only two ways to travel quickly to work in London now. The first is to buy a bike, ignore red lights, no entry signs, one-way streets, pedestrian crossings and pavements, and simply pedal hell-for-leather in a straight line from A to B. The biggest problem with this is that you are likely to fall foul of the only other speedy mode of transport in the capital -- the white van.

White vans -- along with ambassador's cars, black cabs and shopping trolleys -- are exempt from the usual road traffic regulations. If they're not zooming down the bus lanes, they're parked up blocking them (or more usually, they're parked up half on the pavement and half in the bus lane, which amounts to the same thing, only it buggers up the pedestrian traffic as well). If they want to make a right turn half a mile down a road full of stationary traffic, they'll simply pull out and drive down the other side of the road until they can do so. If they want to turn left, they'll do the same sort of thing, cutting back into the line of traffic (and taking out any motorbikes or cyclists that cross their path) at the appropriate moment.

It is mandatory, of course, that no white van may have more than half of its lights working at any one time. Rear indicators and brake lights should either be coated in dirt, broken or left unused as a matter of principle. Since no white van driver can ever see out of the back window, a reverse maneouvre consists of a loud crunching of gears, over-revving of the engine and then a fierce 50-yard acceleration to scare the living daylight out of anyone who happens to be in the way. Ignore those signs painted on the pavement to tell you to look left or right for oncoming traffic. If a white van finds a one-way street going the wrong way to which it wants to go, it simply reverses back up it at speed in the opposite direction.

There are other special rules of the road in London that apply not only to white vans. At any busy junction, for example, a motorist is allowed 10 seconds after the lights turn to red to carry on turning right across the oncoming traffic that is trying to jump a green light to cross your path. It is permitted to park on the yellow zig-zag lines outside schools if you are delivering or picking up children. Anyone with glasses can use disabled parking bays. And if there is nowhere else to park, you can just double up against someone else's vehicle, making sure to move your own the next day in case the other person wants to get out.

It used to be okay, incidentally, to jam a bottle top into a parking meter, put a notice on your car saying that the meter is broken and then enjoy free parking for as long as you like. Recently, though, it has become advisable to remove the whole meter and paint over the yellow lines with black paint. A mechanical angle-grinder is a useful accessory for this sort of activity -- as it is for pedestrians who get fed up of all the cattle fencing that stops them crossing the road where they want to. A couple of judicious cuts to the metal railings and -- hey presto! -- you've got your own personal short cut through the fences across Oxford Circus.

Of course, if you can't face any of this, and the gravity is just too intense down in the Underground, you could always take a train. In fact, in parts of London people have to take a train because the only other alternative would be a bus (and they come in such a dazzling array of different colours and liveries these days that you don't even realise they're buses at all until they've gone sailing past you -- full anyway).

It's a little-known fact that 20 years ago you could get from London to Cardiff by train in 90 minutes, whereas now it takes two hours. It takes roughly the same to get from anywhere in south-east London to anywhere else in the capital. Things were better when they built the first railway here, from Greenwich to London Bridge, about 150 years ago. The fast train could get you to work in the City in about 10 minutes -- and the railway-builders even laid a footpath alongside the railway track so that, for a halfpenny charge, you could walk to work if you wanted instead.

Some bright spark also had the idea of laying a moving track for pedestrians that would be powered by the tidal flow of the Thames, with the track moving towards the City in the mornings and back out again in the afternoons. Apparently the calculations failed on two counts. The Thames' tides didn't fit in with the morning and evening rush hours. And the combined effect of gravity and the weight of all those commuters meant that the track would grind to a standstill on the steeper inclines.

Still, it was a nice idea. And there wasn't a single white van in sight.