How dare I drive a car like this?

Two thousand people protested outside Parliament yesterday in support of the Road Traffic Reduction Bill. Meanwhile, Jonathan Glancey was driving his 1987 Jaguar Sovereign V12 through the City. Here's why

Each time I churn the massive engine of my Jaguar Sovereign into butter-smooth life I commit an act of urban terrorism. The car is the enemy of the city. And few cars this side of an uninsured and untaxed Ford Fiesta loaded to the gunwales with Semtex and parked on double-yellow lines outside the Bank of England are as evil as mine.

How can I possibly justify living in the Dickensian shadow of Smithfield Meat Market, in clear view of St Paul's cathedral, and owning such a gas- guzzling beast? The average speed of road traffic in central London is something like 11mph, but my 10-year-old Jaguar has a top speed of two and a half miles a minute. A seven-ton Routemaster bus (the classic London double-decker) can carry 77 passengers and a crew of two; my two-ton Jag will carry four in luxury, five in comfort and - more often - one in a sybaritic and selfish hush.

Don Foster, Lib Dem MP for Bath, wants cars like my V12 Sovereign banished from our cities. Forever. This week, Mr Foster is power-steering the Road Traffic Reduction Bill through the House of Commons. He is confident that the Government will back this private member's initiative when it comes up for its Second Reading on Friday. "If the Bill becomes law," he says, "it will be one of the most important pieces of transport legislation in the UK. For the first time, the Government will recognise that it needs to tackle the problem of increasing traffic rather than trying to accommodate it."

If triumphant, Foster's Act will be the start of an automotive witch- hunt, an urban Autogeddon. It will require councils to set targets for cutting the numbers of vehicles using towns and cities. It will liberate the pedestrian and cyclist, alleviate congestion (said by Foster to cost British industry pounds 19bn a year) and nurse a polluted nation to health. Fifteen million people are said to be suffering from pollution caused by noxious exhaust fumes.

Cordon off cars from our city centres, the theory is, and we will inherit healthy, safe spaces in which we will pedal, skip and run, clad in liberating leisurewear, where we will ride swish new electric trams, enjoy Venetian views from the sterns of riverboats and sing songs on the top of immaculate and speedy double-decker buses.

Jaguars might fly. The chance of a Bill that curbs the car and thus promotes decent public transport in our cities is a remote one as long as Westminster is committed to the deregulation, or rather break-up, of city bus and rail networks across the country. The retreat of the car is in no way guaranteed to promote excellent public transport in our cities.

My difficulty, and I am pretty sure that I am not alone, is that I want the best possible public transport provision and I want to drive my Jag. If I am prepared to pay the cost, perhaps Mr Foster will make an exception in my (and possibly your) case. The big question is: just how much am I prepared to pay for the luxury of keeping a Jaguar on the road in central London?

Like many motorists, I lie to myself about the cost. I like to say that my Jag has never broken down and that, when all's said and done, it is no more costly than any other car. In any case, I don't drive it in the rush-hour, I don't drive to edge-of-town superstores and DIY warehouses on weekends, I don't do school runs, or even drive to work more than once or twice a month (I can't afford the parking). But if I am honest with myself, I know that the annual costs of Jaguar motoring would pay for all the taxi rides, bus and Tube fares I could want, and still leave me several hundred in change a year.

The reasons to keep on driving are well rehearsed and probably widely shared. The car - in particular a svelte and near-silent walnut and leather- laced Jag - is a retreat from home and office. It has become a mobile study or "den", a music room, somewhere to listen to the radio and escape into our private worlds. More important, I confess, I share the former transport minister Steven Norris's reluctance to sit next to smelly, angry commuters on the bus and Tube. Who doesn't? Each of us finds travelling by public transport aggravating sometimes, if not always. Few of us enjoy sitting next to someone tucking into a foul-smelling burger or shouting inanities into a mobile phone. Only perverts like to be shoved up against the armpit of an overcoat that was last dry-cleaned in 1964.

The great middle class drives to be safe, not from accidents, but from accidental encounters with the rough, the poor and the odoriferous. Executives use the car as a civilised link between well-decorated home, swish office on weekdays and polished superstore on weekends. The car takes them and their gleaming families through twilight zones, muggers, rapists, crazies, Blair's beggars and homeless urchins hawking the Big Issue. Car and car phone (police on tap) keep them safe and warm. Until enough people feel that their city centres are sufficiently clean and secure to walk and bus through with ease, they will stick, wherever feasible, to their cars.

There are other reasons for city dwellers wanting to own a car, but I don't think Don Foster will want to understand these. I could fill many paragraphs singing the praises of my Jaguar and its magnificent engine. It was designed by a brilliant team led by Wally Hassan, whom I met on several occasions. Wally was a Londoner, too. He was born in 1906 in Upper Holloway, north London. His dad ran a clothing shop in Highgate. But, Wally, who died last year, was obsessed by engines, which led to the great V12 Jaguar engine ...

See what I mean? I would choose a Routemaster bus or a 1973 Piccadilly Line Tube train any time over a Ford Yawn or Nissan ZZZZ, but the Jag is a lovely boy's toy. I will only give it up when I have to raid the piggy bank to pay for that last gallon of four-star. I will also continue to champion the best possible public transport for our cities and walk miles every week both to get to work and for pure enjoyment. I will cheer Mr Foster's Bill through even as I fill up the Jag's twin tanks on Clerkenwell Road.

Hypocritical, confused, guilty, I used to think my case was a bit of a special one. Or that there was just me and Steve Norris out there. But perhaps we automotive urban terrorists are as common as a Ford Fiesta.