Like some malign virus, nothing spreads quicker in this place than any new form of criminal maggotry. In the last couple of weeks it's been carjacking, where unsuspecting motorists have been forced to hand over their vehicles to weapon-wielding thugs.

I have such sympathy for the people - mostly women - who have fallen victim to this. A few years back I almost got carjacked myself.

As with some of the more recent incidents it happened in January in broad daylight - or in as broad daylight as you get mid-afternoon at this time of the year - and right in the city centre.

I made the mistake (hands up) of jumping out of my car to shut a car park gate behind me.

I left the keys in the ignition. (None of the more recent victims had been similarly careless.)

It was a stupid thing to do. But then you don't always think the next person coming ambling along the street is likely to be a car thief. In my case there were two of them. A chunky looking big yob and his more weedy sidekick.

Out of the corner of my eye I saw one nudge the other and nod towards the car and in that awful moment I knew what they were going to do. We were all a few yards off the vehicle. We all ran.

The big guy got there first. He half jumped in. I half jumped in on top of him.

I don't know who was most shocked by this. Possibly me. What was I thinking? Short answer - I wasn't thinking at all.

It was total instinct. What the car salesmen would call cruise control.

If there was any thought process at all it was a wave of what I can best describe as self-recrimination.

You've done a really, really stupid thing. Now try to redress the situation.

And yes, I know tackling car thieves is even more stupid still. I just wasn't thinking. I was totally focused on one thing.

Get the key out of the ignition.

In an odd silence punctuated only by grunts, both of us tussled for the keys. I got there first this time.

Outside the car the ineffectual sidekick began banging the car door against my legs. I didn't even feel it. At the time.

Wimp that he was, he leapt back as I (now finally, frightened) jumped out of the car. The bigger guy clambered out. He didn't look like such a pushover ...

And then miraculously the cavalry appeared. A young couple coming down the street had spotted us. The lad (I never even got his name) yelled and started to run at the yobs. They fled like the vermin they were.

What I have learned from this incident?

Sadly nothing, I suspect. My fear is that in a similar situation I'd do exactly the same thing again because instinct does take over.

And that's why I worry that the current spate of obviously copycat attacks could so easily end in tragedy.

The yobs themselves are gutless cowards. We all know that. They target women. Motorists on their own. They are armed. And because what they are at is premeditated they are undoubtedly more dangerous than my would-be car-jackers.

What are the police doing to counter them? More patrols, more visibility on the streets would be reassuring.

You would like to think that CCTV would be a useful deterrent too. (We're endlessly told we're constantly being watched by countless lenses.)

But how good is it really?

Thus far it doesn't appear to have been much help in curtailing this latest trend in car crime.

The potential for tragedy here is enormous. Telling women to lock themselves in their cars (as the police have done) just isn't enough.

Right now we need to be assured it's the cops - not the criminals - who are in the driving seat.