Long before people were talking about carbon footprints and renewable energy and things like that, I was bicycling around London. And my reasons for doing so were --although I did not, and do not, talk in that kind of tiresome jargon -- rather environmentally conscious, and socially aware, too.

If there is one subject we hear more about in Britain than global warming it is obesity. Week by week the gloomy results of a sedentary culture are revealed: 700,000 morbidly obese Britons need stomach stapling; one in four younger adolescents are obese; half of young boys could be dangerously overweight by 2050… Why? Because they eat too much and spend too much time in front of small screens. Relatively few know the pleasures of daily outdoor play or flying downhill on a bike.

If more of us took to our bikes, we would begin to see that a lot of car journeys aren't necessary. 

Back in the 1970s when I got my first earnings I bought my first bicycle. I will never forget the thrill of it. I hadn't had a bike as a child as we lived near a main road and my parents did not let us go out and about like that; we had scooters and tricycles for the (large) garden and were perfectly content with those.

Oh, the joy that a bicycle brought! I had taken some driving lessons and loathed them. Always carsick as a child, I was reliably informed -- and have since found that it is true for many people -- that all nausea fades when you are at the wheel, concentrated and in charge. But it didn't work like that for me and each lesson increased my misery, not only because I was dreadfully bad at driving, but also because it was beginning to commit me to the whole motorised scene: the smell of petrol, the smell of the inside of a car on a hot day, the going round and round looking for parking spaces, the worry of all that powerful force in my nervous hands and no one able to stop me when things got out of control.

So when my father, who was paying for the lessons, gently suggested that the options were (a) to take the lessons more seriously, work hard and pass the driving test or (b) stop wasting time and money now, I opted for (b) with enthusiasm. But I didn't want to be a boring drain on everyone else's time and car-driving skills. I got a bike, I walked, I took trains, and decided that as an adult these would be my main forms of transport.

The reasons for my choice were, and are, larger too. Heartbreakingly beautiful stretches of glorious countryside have been crunched into concrete swirls as motorways curl over England, disgorging more and more vehicles into town centres that can't accommodate them. The carnage (a word destined to reveal its full meaning in the 20th century) from road accidents is huge and would be regarded as outrageous if it happened on the railways.

People drive when they don't really need to; a neighbour in our street when I was a teenager used to drive to the shop at the end of the road, a distance of only a few yards. They bundle children into cars and take them on long shopping forays, bribing them with toys and sweets when they wail about it. Ironically, a major reason given for not sending children outside to play is that there is too much traffic.

I know all the arguments in favour of cars and I go along with them. My husband drives a car. It's very convenient for our trips down to the West Country with camping equipment for holidays and visits to relations. It's a boon for transporting my elderly mother. There are lots of things we couldn't have done without a car, such as getting new dining-room chairs from a second-hand shop in a neighbouring suburb and ferrying ourselves and others to remote places where there are no trains or buses. I was rescued once by car from a Norfolk town where the next bus to the village I wanted was not due for several more days. Cars are useful and necessary.

But how many cars does a busy couple need? In a city with an underground rail system, buses, trains, and taxis? Where there are pavements on which one can walk, and short-cuts through parks and along agreeable routes for the knowledgeable?

I don't lead a leisurely lifestyle. I hurry. My bike whizzes me past traffic queues to appointments. It gets put on trains, although this is banned in London's rush hour - an irritating but probably necessary restriction. It can be padlocked and left while I nip into a committee meeting, conference, coffee morning, party or babysitting session, with no time lost in searching for a parking-space.

Oh yes, there is a downside. I have had bikes stolen (five, to date). I've had them vandalised (attempts to remove front wheel, lamps stolen, basket ripped, pump stolen). I've known all the disadvantages of cycling (wet weather, dirt, dust in eyes and mouth and nose, misery of toiling uphill in heat, downhill in icy conditions). And I admit to having contributed to the misery of others by doing the nasty things that cyclists do: suddenly popping up on to a deserted pavement to avoid a long queue of traffic, converting to pedestrian status to walk across at a busy set of traffic lights while drivers fume and wait, nipping into a park and careering merrily along without keeping to the cycle track. I don't always check my lights, wear bright clothing, or take enough care for others on the road. I know, I know.

But I honestly do believe that cycling is a Good Thing. If more of us took to our bikes, we would begin to see that a lot of car journeys aren't necessary. It is true that you can carry less shopping (though a knapsack and a basket can carry a lot). But it's also a truism that much of the food we buy gets thrown away in any case; do we really need jumbo-sized packets, buy-one-get-one-free, of everything? Might not a bikeload be an appropriate amount of family shopping, rather than a carload? And if more than one trip to the shops was necessary each week, would that be so terrible? Especially if it meant that local shops got supported?

Let me repeat, I am not against cars as such. Even motorways bring pleasure in that they whiz us to holidays, family reunions and interesting events. It's great that we can rush to doctors and dentists and hospitals. A car is invaluable for people who would otherwise be stuck at home -- I have a wheelchair-bound friend who drives himself and his friends about and whose life would be horribly limited without his car. My childhood holiday memories are bound up with the excitement of the family car, packed with equipment and clothes and towels and bedding, trundling over the South Downs with excited children on board and resounding with gleeful shouts as we first saw the sea. I have been grateful, times without number, for the sight of my husband in our car, and we've had some trips to lovely places together.

But if we want to preserve what is left of our glorious countryside, enjoy the pleasures of the passing seasons (some car-bound children barely notice if it's raining, or frosty, or a sweet-scented spring morning), conquer obesity and save the planet, why don't we just get on our bikes?

Joanna Bogle writes from London.